Error-code hub

Mitsubishi Electric error codes

Mitsubishi Electric systems report faults two ways: M-Series wall units flash the operation and timer LEDs in a counted pattern, while MXZ multi-zone condensers and wired controllers show an alphanumeric code directly. The 59 codes below are drawn from Mitsubishi's own service documentation. Note that Trane's ML Series is Mitsubishi-built, so its codes closely resemble these - but check the Trane pages for that brand's own wording.

See Mitsubishi Electricmini-splits ->Common First Status Displays Error Codes

Status displays: 14
Error codes: 59

Unit applicability

Match your unit before reading the table

This hub has separate sourced tables for M-Series GX and MXZ-D Ported Multi-Zone. Select the product line that matches your indoor or outdoor unit before comparing codes.

M-Series GX12 models MXZ-D Ported Multi-Zone5 models

Common codes first

Most broadly applicable documented codes

Ranking basis: we do not have failure-frequency telemetry. These are ordered by breadth of affected systems in the SplitAtlas catalog - the documented product line's published model count, whether the same code appears on more than one product line, and any manual applicability notes we hold. This is a breadth ranking, not a popularity claim.

E6 means the indoor head stopped receiving the outdoor unit serial communication signal. To a homeowner, that usually means the two halves of the mini split are powered but are no longer confirming each other. The code does not identify which side failed; it tells you the communication path needs diagnosis if one reset does not hold. Manual trigger: Serial signal from the outdoor unit is not received by the indoor unit for a maximum of 6 minutes.

AdvisoryTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric MSZ-GX R454B wall-mounted indoor units covered by OBH950B; common M-Series wall-mount diagnostics apply where matched by model manual.
Safe first check: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

View the fix

E7 means the indoor and outdoor units are not exchanging serial communication normally. The system cannot trust the conversation between the two units, so it stops instead of running blind. A reset can clear a temporary handshake fault, but repeated E7 is a wiring or board diagnosis. Manual trigger: Serial signal communication between the indoor and outdoor units is abnormal.

AdvisoryTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric MSZ-GX R454B wall-mounted indoor units covered by OBH950B; common M-Series wall-mount diagnostics apply where matched by model manual.
Safe first check: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

View the fix

E8 means the indoor and outdoor controls are not exchanging a signal the system can trust. That can be a simple power-handshake problem, but repeated communication faults usually point to wiring, connectors, or a control board. One reset is reasonable; repeated resets are not a fix. Manual trigger: Any signal from the inverter P.C. board cannot be received normally for 3 minutes.

AdvisoryTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric M-Series R454B wall-mount outdoor units covered by MUZ-GX OBH951C and cross-checked against MUZ-FX OBH946C and MUZ-WX OBH955A.
Safe first check: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

View the fix

E9 means the indoor and outdoor controls are not exchanging a signal the system can trust. That can be a simple power-handshake problem, but repeated communication faults usually point to wiring, connectors, or a control board. One reset is reasonable; repeated resets are not a fix. Manual trigger: The outdoor inverter sends signal 0 but signal 1 is received 30 consecutive times.

AdvisoryTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric M-Series R454B wall-mount outdoor units covered by MUZ-GX OBH951C and cross-checked against MUZ-FX OBH946C and MUZ-WX OBH955A.
Safe first check: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

View the fix

EC means the indoor and outdoor controls are not exchanging a signal the system can trust. That can be a simple power-handshake problem, but repeated communication faults usually point to wiring, connectors, or a control board. One reset is reasonable; repeated resets are not a fix. Manual trigger: The start-up process of the outdoor unit does not complete for 4 minutes.

AdvisoryTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric M-Series R454B wall-mount outdoor units covered by MUZ-GX OBH951C and cross-checked against MUZ-FX OBH946C and MUZ-WX OBH955A.
Safe first check: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

View the fix

EE means the indoor and outdoor units are not an allowed refrigerant-type or model combination. This is not wear and tear; it usually points to an installation, replacement, or pairing problem. Running mismatched equipment can create reliability and safety problems. Manual trigger: The refrigerant types specified for the connected indoor and outdoor units do not match.

Stop useTechnician

Breadth evidence: 12 published catalog models on its documented product line. Manual applicability notes: Mitsubishi Electric MSZ-GX R454B wall-mounted indoor units covered by OBH950B; common M-Series wall-mount diagnostics apply where matched by model manual.
Safe first check: Turn the system off and do not keep testing modes or resets. Expected result: the compressor and electronics are protected until the installation or equipment mismatch is corrected.

View the fix

Safe first checks

Checks you can do without opening the unit

These codes have homeowner-safe steps such as filters, airflow, condensate/drain checks, remote/controller items, or a single safe power reset. If the code returns, stop at the boundary in the card.

P8DIY part

Clean the indoor filters. If the air-cleaning filter is packed with dust, tobacco tar, oil, or damage that cleaning will not remove, replace that user-serviceable filter before resetting once. Make sure louvers and return air are not blocked. Expected result: if airflow recovers, the code clears; if P8 returns, stop there.

Sourced homeowner part

Mitsubishi microparticle filter

View sourced part route

Read the full code guide

E6Technician

Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.

Read the full code guide

E7Technician

Read the full code guide

E8Technician

Read the full code guide

Mitsubishi Electric mini-splits

Use the Mitsubishi Electric catalog to connect these manual error codes to current model pages and replacement options.

See Mitsubishi Electricmini-splits ->

Status displays

00

00 means the controller has no current matching memorized error. The system is not reporting an active fault from that recall screen.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: No repair action is needed. If the system is comfortable and running normally, leave it alone.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LAST ERROR STORED

The remote can show the last memorized error even after the current fault has cleared. This is history, not proof that the system is still broken right now.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Observe current operation and write down the stored code for the technician if service is already scheduled.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 1 BLINK AND LED2 LIT

This MXZ-D operating indication means primary current protection is limiting operation while the unit still runs. The manual notes this does not mean the product is abnormal by itself.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Check filters and indoor/outdoor airflow. If the system remains comfortable and the indication clears, no repair is needed.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 2 BLINKS AND LED2 LIT

This MXZ-D operating indication points to heating high-pressure control or cooling defrosting control while the unit operates. It can be a normal protection/control state.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Check filters and airflow, then observe. Call for service only if comfort is poor or the indication repeats with shutdowns.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 5 BLINKS AND LED2 LIT

This MXZ-D operating indication means cooling high-pressure protection is active while the unit operates. The manual frames it as not automatically abnormal.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Check filters, indoor airflow, and outdoor clearance. Call for service if it repeats or the unit stops cooling.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 7 BLINKS AND LED2 LIT

This MXZ-D operating indication is a pressure-bypass or evaporating-temperature drop prevention control. It is a protective operating state, not automatically a fault.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Observe operation and comfort. Call for service if the system cannot condition the zones.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 8 BLINKS AND LED2 LIT

This MXZ-D operating indication means cooling evaporating-temperature protection is active. It is a control response while the unit operates.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Check filters and airflow. Call for service if it repeats with poor cooling.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 9 BLINKS AND LED2 LIT

This MXZ-D indication is inverter check mode during emergency operation. It is expected only when that service or emergency mode is being used.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: If emergency operation was not intentional, exit that mode or call the installer to confirm the control state.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

LED1 LIT AND LED2 LIT

LED1 lit and LED2 lit is the normal outdoor control board indication for this MXZ-D table. It is not an error by itself.

Not an error

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: No repair action is needed if the system is operating normally.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

MXZ MODE CONFLICT

MXZ mode conflict means indoor heads are asking for incompatible modes, such as one zone calling for cooling while another calls for heating. That is a coordination status, not a failed part.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Set all connected indoor heads to the same mode, then wait several minutes for operation to resume.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

OUTDOOR LED 1 BLINK (OPERATES)

This operating indication means the compressor frequency is being reduced by current protection control. The manual frames it as a normal control response while the unit continues operating.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Check filters and indoor/outdoor airflow. If comfort is normal and the indication clears, no repair is needed.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

OUTDOOR LED 3 BLINK (OPERATES)

This operating indication means the system is reducing output for high-pressure protection or indoor-coil overcooling prevention. It is a control response, not automatically a failure.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean filters and confirm indoor and outdoor airflow are not blocked. Call for service if comfort is poor or it repeats often.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

OUTDOOR LED 4 BLINK (OPERATES)

This operating indication means compressor frequency is being reduced by discharge-temperature protection. The unit is still operating but protecting itself from heat stress.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clear outdoor airflow and clean filters. Call for service if it repeats or the system cannot satisfy the room.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

OUTDOOR LED LIT

A steady outdoor LED can be a normal outdoor board indication during operation. By itself, it is not an error code.

Not an error

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: No repair action is needed if the unit is heating or cooling normally.
Status note: This is a normal status indication, not an error, unless comfort is poor or the indication never clears.

View the fix ->

Error codes by unit family

Choose the product line that matches your unit, then use the full code list below. The catalog is preserved; the grouping is only to keep generation and model applicability visible.

M-Series GX

32 error codes / 12 catalog models tied to this line.

EE

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off and do not keep testing modes or resets. Expected result: the compressor and electronics are protected until the installation or equipment mismatch is corrected.
When to call a pro: Call the installing contractor, Mitsubishi dealer, or licensed HVAC technician before running it again. Tell them the exact Mitsubishi stop-use code and whether installation or service happened recently.

View the fix ->

FD

FD means the outdoor unit is connected to the wrong supply voltage. This is not a nuisance code; wrong voltage can damage the inverter and compressor. Leave the system off until the electrical supply and model requirements are verified.

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off and do not keep testing modes or resets. Expected result: the compressor and electronics are protected until the installation or equipment mismatch is corrected.
When to call a pro: Call the installing contractor, Mitsubishi dealer, or licensed HVAC technician before running it again. Tell them the exact Mitsubishi stop-use code and whether installation or service happened recently.

View the fix ->

FH

FH means the refrigerant sensor is not working, not connected, or has a broken wire. Even when it is a sensor fault rather than a confirmed leak, the system has lost an important R454B safety monitor. Do not run it as normal until the sensor circuit is confirmed.

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Ventilate the room, avoid flames or spark sources, let any automatic fan safety operation run, and do not use normal heating or cooling. Expected result: people are protected while a qualified technician verifies the leak or sensor condition.
When to call a pro: Call a licensed HVAC technician before using the system normally. Tell them the exact Mitsubishi code and that it involves R454B refrigerant detection, leak sensing, or refrigerant-system abnormality.

View the fix ->

FL

FL means the indoor refrigerant sensor detected refrigerant leakage. Because these current Mitsubishi systems use R454B, the alarm deserves immediate safety treatment even if you do not smell anything. Ventilation and a qualified technician matter more than clearing the code. Manual trigger: The indoor refrigerant sensor detects refrigerant leakage.

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Ventilate the room, avoid flames or spark sources, let any automatic fan safety operation run, and do not use normal heating or cooling. Expected result: people are protected while a qualified technician verifies the leak or sensor condition.
When to call a pro: Call a licensed HVAC technician before using the system normally. Tell them the exact Mitsubishi code and that it involves R454B refrigerant detection, leak sensing, or refrigerant-system abnormality.

View the fix ->

PL

PL means the outdoor unit detected a refrigerant-system abnormality, with the manual pointing to conditions such as a closed valve or trapped air. For a homeowner, the important point is that refrigerant flow is not normal and continued operation can damage the system. Treat it as a stop-and-call code, not a reset-and-ignore code. Manual trigger: The outdoor unit detects an outdoor refrigerant-system abnormality, including closed valve or trapped air conditions.

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Ventilate the room, avoid flames or spark sources, let any automatic fan safety operation run, and do not use normal heating or cooling. Expected result: people are protected while a qualified technician verifies the leak or sensor condition.
When to call a pro: Call a licensed HVAC technician before using the system normally. Tell them the exact Mitsubishi code and that it involves R454B refrigerant detection, leak sensing, or refrigerant-system abnormality.

View the fix ->

UE

UE means the outdoor unit detected a stop-valve or closed-valve condition. That can prevent refrigerant from moving correctly and can damage the compressor if the system keeps trying to run. This is especially important after installation, service, or a recent move of the outdoor unit. Manual trigger: The outdoor unit detects a stop-valve or closed-valve condition.

Stop useTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off and do not keep testing modes or resets. Expected result: the compressor and electronics are protected until the installation or equipment mismatch is corrected.
When to call a pro: Call the installing contractor, Mitsubishi dealer, or licensed HVAC technician before running it again. Tell them the exact Mitsubishi stop-use code and whether installation or service happened recently.

View the fix ->

E6

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

View the fix ->

E7

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

View the fix ->

E8

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

View the fix ->

E9

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

View the fix ->

EC

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

View the fix ->

FB

FB means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: The indoor electronic control P.C. board cannot read nonvolatile memory data properly.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

View the fix ->

FC

FC means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: The outdoor inverter P.C. board cannot read nonvolatile memory data properly.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

View the fix ->

P1

P1 means a temperature sensor reading does not make sense to the control board. The system uses those sensors to decide when to heat, cool, defrost, and protect itself, so it may stop even if the room feels normal. Filters and airflow are worth checking, but sensor circuits are technician work. Manual trigger: The room temperature thermistor is detected shorted or open every 8 seconds during operation.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and make sure the indoor filter and nearby airflow are not obviously blocked. Expected result: a temporary sensor fault clears; if the same code returns, the sensor circuit needs service.
When to call a pro: Call a licensed HVAC technician if the code comes back after one reset or the unit will not heat or cool normally. Tell them which thermistor-related Mitsubishi code is displayed.

View the fix ->

P2

P2 means a temperature sensor reading does not make sense to the control board. The system uses those sensors to decide when to heat, cool, defrost, and protect itself, so it may stop even if the room feels normal. Filters and airflow are worth checking, but sensor circuits are technician work. Manual trigger: An indoor coil thermistor is detected shorted or open every 8 seconds during operation.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and make sure the indoor filter and nearby airflow are not obviously blocked. Expected result: a temporary sensor fault clears; if the same code returns, the sensor circuit needs service.
When to call a pro: Call a licensed HVAC technician if the code comes back after one reset or the unit will not heat or cool normally. Tell them which thermistor-related Mitsubishi code is displayed.

View the fix ->

P4

P4 means the indoor unit sees a drain, drain-sensor, or indoor valve signal problem. If water cannot leave the unit or a drain sensor cannot be trusted, the system may stop to prevent overflow or abnormal operation. Check for visible water or a blocked drain outlet only from outside the cabinet. Manual trigger: Drain sensor connector CN1S1 is open for more than 3 minutes.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: If you see water at the indoor head, turn the system off. Check only for an obvious blocked drain outlet or overflowing pan; if water is present or the code remains, leave it off.
When to call a pro: Call a licensed HVAC technician if water is present, the indoor head is dripping, or the code returns. Tell them the code points to the drain sensor, drain pump, or indoor LEV/drain circuit.

View the fix ->

P9

P9 means a temperature sensor reading does not make sense to the control board. The system uses those sensors to decide when to heat, cool, defrost, and protect itself, so it may stop even if the room feels normal. Filters and airflow are worth checking, but sensor circuits are technician work. Manual trigger: The alternate indoor coil thermistor code is detected for the indoor coil thermistor short/open condition.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and make sure the indoor filter and nearby airflow are not obviously blocked. Expected result: a temporary sensor fault clears; if the same code returns, the sensor circuit needs service.
When to call a pro: Call a licensed HVAC technician if the code comes back after one reset or the unit will not heat or cool normally. Tell them which thermistor-related Mitsubishi code is displayed.

View the fix ->

PB

PB means the indoor blower is not operating or reporting speed normally. If the blower cannot move air across the coil, heating and cooling performance can fall quickly and the system may protect itself. Filters and visible blockage are safe to check; motor and board diagnosis is professional work. Manual trigger: Indoor fan motor feedback signal is not emitted for 12 seconds while the fan motor operates.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the unit off, clean the indoor filter, and check only for obvious visible blockage at the air outlet. Restart once; if the blower does not run normally, stop troubleshooting.
When to call a pro: Call a licensed HVAC technician if the blower is noisy, stuck, or the code returns. Tell them the unit reported an indoor fan feedback fault.

View the fix ->

U3

U3 means a temperature sensor reading does not make sense to the control board. The system uses those sensors to decide when to heat, cool, defrost, and protect itself, so it may stop even if the room feels normal. Filters and airflow are worth checking, but sensor circuits are technician work. Manual trigger: The discharge temperature thermistor shorts or opens during compressor operation.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and make sure the indoor filter and nearby airflow are not obviously blocked. Expected result: a temporary sensor fault clears; if the same code returns, the sensor circuit needs service.
When to call a pro: Call a licensed HVAC technician if the code comes back after one reset or the unit will not heat or cool normally. Tell them which thermistor-related Mitsubishi code is displayed.

View the fix ->

U4

U4 means a temperature sensor reading does not make sense to the control board. The system uses those sensors to decide when to heat, cool, defrost, and protect itself, so it may stop even if the room feels normal. Filters and airflow are worth checking, but sensor circuits are technician work. Manual trigger: An outdoor thermistor circuit is shorted or open.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and make sure the indoor filter and nearby airflow are not obviously blocked. Expected result: a temporary sensor fault clears; if the same code returns, the sensor circuit needs service.
When to call a pro: Call a licensed HVAC technician if the code comes back after one reset or the unit will not heat or cool normally. Tell them which thermistor-related Mitsubishi code is displayed.

View the fix ->

U6

U6 points to the power module or compressor winding short-circuit path. This is a serious compressor-drive fault, not a cleaning or settings issue. The system may refuse to run because continuing could damage expensive outdoor electronics. Manual trigger: The manual identifies power module abnormality or compressor winding short circuit.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off for 2 minutes, restore power once, and listen for normal startup. If the code returns, do not keep trying to force the compressor to start.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, the outdoor unit hums or clicks, or the breaker trips. Tell them the code is tied to compressor, IPM, inverter, or startup protection.

View the fix ->

U8

U8 means the outdoor fan is not operating or reporting back the way the controls expect. Without the outdoor fan, the coil cannot move heat normally, so the system may shut down to protect itself. Keep leaves, snow, and debris away, but motor and board checks belong to a technician. Manual trigger: The outdoor fan motor is detected as abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn power off before looking at the outdoor fan area. Remove only obvious loose debris outside the grille, restore power once, and stop if the code returns or the fan does not start.
When to call a pro: Call a licensed HVAC technician if the fan is not visibly blocked, the fan blade is damaged, or the code returns. Tell them the Mitsubishi code identifies the outdoor fan motor circuit.

View the fix ->

UF

UF means the outdoor unit is protecting the compressor or inverter drive. Homeowner checks are limited because the expensive parts are inside the outdoor cabinet. If one reset does not hold, the compressor-drive circuit needs professional diagnosis. Manual trigger: The outdoor unit detects overcurrent, compressor synchronous abnormality, or start-up failure.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off for 2 minutes, restore power once, and listen for normal startup. If the code returns, do not keep trying to force the compressor to start.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, the outdoor unit hums or clicks, or the breaker trips. Tell them the code is tied to compressor, IPM, inverter, or startup protection.

View the fix ->

UH

UH means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: Each phase current of the compressor cannot be detected normally.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

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UJ

UJ means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: Abnormal DC bus-bar voltage is detected by the inverter system.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

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UP

UP means the outdoor unit is protecting the compressor or inverter drive. Homeowner checks are limited because the expensive parts are inside the outdoor cabinet. If one reset does not hold, the compressor-drive circuit needs professional diagnosis. Manual trigger: Overcurrent protection cut-out operates 3 consecutive times within 1 minute after compressor start.

AdvisoryTechnician

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Turn the system off for 2 minutes, restore power once, and listen for normal startup. If the code returns, do not keep trying to force the compressor to start.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, the outdoor unit hums or clicks, or the breaker trips. Tell them the code is tied to compressor, IPM, inverter, or startup protection.

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P8

P8 means the system saw pipe temperature behavior that does not match normal operation. In homeowner terms, the indoor coil temperature is not changing the way the controls expect during heating or cooling. Filters and airflow are the safe checks; thermistor, refrigerant-flow, and inverter diagnosis belong to a technician. Manual trigger: The pipe-temperature abnormality protection is detected.

AdvisoryDIY part

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters. If the air-cleaning filter is packed with dust, tobacco tar, oil, or damage that cleaning will not remove, replace that user-serviceable filter before resetting once. Make sure louvers and return air are not blocked. Expected result: if airflow recovers, the code clears; if P8 returns, stop there.
When to call a pro: Call a licensed HVAC technician if P8 returns after filters and airflow are corrected or if the system still blows room-temperature air. Tell them P8 is a pipe-temperature abnormality and when it appears in the cycle.

Sourced homeowner part

Mitsubishi microparticle filter

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U2

U2 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The discharge temperature exceeds 241F (116C) during compressor operation.

AdvisoryDIY

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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U5

U5 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The fin temperature protection threshold is exceeded during compressor operation.

AdvisoryDIY

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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U7

U7 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The discharge temperature is lower than the manual target condition.

AdvisoryDIY

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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UB

UB means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The outdoor P.C. board temperature protection threshold is exceeded during compressor operation.

AdvisoryDIY

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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UD

UD means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The outdoor unit enters high pressure protection.

AdvisoryDIY

Sourced Jul 2026

Applies to: M-Series GX
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

Technician part context

Mitsubishi M-NET Interface for MXZ

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MXZ LED2 12

MXZ LED2 12 means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: The zero-cross detecting circuit is abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

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MXZ LED2 13

MXZ LED2 13 means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: The input-current detection circuit is abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

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MXZ LED2 14

MXZ LED2 14 means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: The input-voltage detection circuit is abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

View the fix ->

MXZ LED2 15

MXZ LED2 15 means a control-board memory, voltage, or feedback signal is outside the normal range. That does not tell a homeowner which board is bad; it tells you the controls are no longer confident enough to run normally. Treat a repeat code as a service diagnosis. Manual trigger: Relay operation is not detected normally.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Power cycle once and note any storm, brownout, generator, or recent electrical work. Expected result: a one-time control fault clears; if it returns, do not open the cabinet.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset or you suspect a supply-voltage problem. Tell them the Mitsubishi code points to a board, relay, current, voltage, or converter circuit.

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MXZ LED2 21

MXZ LED2 21 means the outdoor unit did not confirm normal reversing-valve operation. That valve is what lets a heat pump switch between heating and cooling, so the symptom may look like poor heating, poor cooling, or room-temperature air. This is not a homeowner repair. Manual trigger: The 4-way valve is detected abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Power cycle once and confirm all indoor heads are set to a compatible mode. Expected result: the fault clears; if heating and cooling still do not switch normally, stop there.
When to call a pro: Call a licensed HVAC technician if the code returns or the unit cannot change between heating and cooling. Tell them the code points to 4-way valve operation.

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MXZ LED2 24

MXZ LED2 24 means the indoor and outdoor controls are not exchanging a signal the system can trust. That can be a simple power-handshake problem, but repeated communication faults usually point to wiring, connectors, or a control board. One reset is reasonable; repeated resets are not a fix. Manual trigger: Serial signal communication between indoor and outdoor units is abnormal.

AdvisoryTechnician

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Turn the system off, switch the breaker or disconnect off for 2 minutes, then restore power and call for one mode only. Expected result: the code clears and the indoor and outdoor units start normally; if it returns, stop resetting.
When to call a pro: Call a licensed HVAC technician if the code returns after one reset, either unit remains dead, or a breaker trips. Tell them the exact Mitsubishi code and that it points to a serial/control communication path.

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MXZ LED1 03

MXZ LED1 03 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The MXZ-D outdoor unit entered discharge temperature protection.

AdvisoryDIY

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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MXZ LED1 04

MXZ LED1 04 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The MXZ-D outdoor unit entered fin or P.C. board temperature protection.

AdvisoryDIY

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

View the fix ->

MXZ LED1 05

MXZ LED1 05 means the system hit a temperature or pressure protection limit. That often means the unit is trying to protect the compressor rather than keep forcing operation. Dirty filters, blocked airflow, outdoor obstruction, weather, or refrigerant-flow problems can be involved. Manual trigger: The MXZ-D outdoor unit entered high pressure protection.

AdvisoryDIY

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Clean the indoor filters, clear leaves or snow around the outdoor unit, confirm supply and return air are not blocked, then reset once. Expected result: the protection clears and does not return during the next heating or cooling call.
When to call a pro: Call a licensed HVAC technician if the code returns after filters and airflow are corrected, or if cooling/heating is weak. Tell them the code appeared with a temperature or pressure protection condition.

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MXZ LED1 11

MXZ LED1 11 means low outside-temperature protection stopped the outdoor unit. This can be a normal protection response when conditions are outside the unit operating envelope. If outdoor temperature is within the published operating range and it still appears, sensors or controls need service.

AdvisoryDIY

Sourced Jul 2026

Applies to: MXZ-D Ported Multi-Zone
Homeowner fix: Confirm the outdoor unit is not buried in snow or ice and wait for outdoor temperature to move back within operating range. Do not force emergency operation repeatedly.
When to call a pro: Call a licensed HVAC technician if the code appears when outdoor temperature is within the published range or the unit cannot heat in normal conditions. Tell them the MXZ-D is showing low outside-temperature protection.

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