Your Mitsubishi aircon is showing an error code (like P1, E6, U2) or a flashing LED pattern on the indoor unit, and you need to know what it means. You need three things: how to read the code on your specific Mitsubishi remote, what each code actually represents, and whether you can fix it yourself or need to call a technician.
This guide answers all three. At Lion City Aircon, we’ve serviced over 22,000 aircon units across Singapore since 2016, including thousands of Mitsubishi Electric (Starmex) and Mitsubishi Heavy Industries (Mr.Slim, City Multi) systems. This page is based on Mitsubishi’s official service manuals cross-checked against what we actually see in Singapore homes and offices.
Jump to your section:
- How to Display Your Mitsubishi Error Code
- Residential / Mr.Slim Quick Reference
- Detailed Mr.Slim Code Sections
- Commercial / City Multi Quick Reference
- Repair Cost in Singapore
- Frequently Asked Questions
How to Display Your Mitsubishi Error Code
Mitsubishi uses two main code systems in Singapore: the Mr.Slim system (used on Starmex residential splits and Mr.Slim commercial light units) and the City Multi system (used on commercial VRF installations in offices and shops). Codes display differently depending on whether you have a wired or wireless remote.
Wired Remote Controller (PAR-31MAA, PAR-32MAA, PAR-40MAA)
These are the standard wired remotes on Mitsubishi systems.
- When the indoor unit detects a fault, the CHECK indicator on the remote screen lights up.
- The error code displays alongside the indoor unit number (e.g., “P1 / Unit 1”).
- Press the CHECK button (sometimes labelled “Inspection” or accessed through the menu on newer remotes) to retrieve stored fault history.
- Use the temperature up/down arrows to scroll through past errors if multiple are logged.
- To clear the error log, hold the ON/OFF button for 4 seconds while in check mode (on PAR-31 and later models).
Wireless Remote (Standard Starmex Residential)
For the standard wireless remotes that come with Mitsubishi Starmex residential aircons in Singapore.
- When a fault is active, the OPERATION INDICATOR lamp on the indoor unit flashes a specific number of times, then pauses, then repeats.
- Count the number of flashes between pauses. Each number corresponds to a fault code. The Mr.Slim quick reference table below shows the mapping.
- The indoor unit also beeps the same number of times as the LED flashes.
- For example: 1 flash equals P1 (intake sensor error), 2 flashes equals P2 (pipe sensor error), 6 flashes equals P4 (float switch error).
Reading the Outdoor Unit’s LED (Mr.Slim Outdoor)
If your indoor unit shows no code but the outdoor isn’t working properly, check the LED on the outdoor unit’s control board:
- 1 flash per 2.5-second cycle: Outdoor power system fault
- 2 flashes: Outdoor thermistors fault
- 3 flashes: Outdoor control system fault
- 4 flashes: Serial signal fault (indoor/outdoor communication)
- 5 flashes: Compressor or stop valve issue
- 6 flashes: Discharge temperature overheat protection
- 7 flashes: Heatsink temperature protection
- 8 flashes: High pressure protection or outdoor fan motor issue
- 10 flashes: Outdoor fan motor fault
- 11 flashes: Compressor phase current fault
How to Read a Mitsubishi Error Code
Mitsubishi residential codes use a letter-and-character format:
- P codes: Errors detected by the indoor unit (sensors, drainage, fan motor, refrigerant cycle)
- E codes: Communication errors (indoor-outdoor, indoor-remote, indoor-indoor)
- U codes: Outdoor unit faults (compressor, thermistors, pressure, power)
- F codes: Indoor control system errors (memory, PCB)
City Multi commercial systems use 4-digit numeric codes (e.g., 1102, 1302, 2502, 4220). These appear on wired remotes connected to commercial installations. Most Singapore homes won’t see these.
Mr.Slim Residential Quick Reference Table
Indoor Unit Errors (Output Pattern A)
| Wired R/C Code | Wireless Flash Count | What it Means | Severity |
|---|---|---|---|
| P1 | 1 flash | Intake sensor error | Medium |
| P2 | 2 flashes | Pipe (TH2) sensor error | Medium |
| P9 | 2 flashes | Pipe (TH5) sensor error | Medium |
| E6, E7 | 3 flashes | Indoor/outdoor unit communication error | High |
| P4 | 4 flashes | Float switch connector open / drainage issue | Medium |
| P5 | 4 flashes | Drain pump error | Medium |
| PA | 4 flashes | Forced compressor error (water leakage abnormality) | High |
| P6 | 5 flashes | Freeze protection (cooling) / Overheat protection (heating) | Medium |
| EE | 6 flashes | Combination error between indoor and outdoor unit | High |
| P8 | 7 flashes | Pipe temperature error | Medium |
| E4, E5 | 8 flashes | Communication error between wired remote and indoor unit | Medium |
| PB (Pb) | 9 flashes | Indoor unit fan motor error | High |
| FB (Fb) | 10 flashes | Indoor unit control system error (memory) | High |
| PL | 11 flashes | Refrigerant circuit abnormal | High |
| E0, E3 | 12 flashes | Remote controller transmission error | Medium |
| E1, E2 | 14 flashes | Remote controller control board error | Medium |
Outdoor Unit Errors (Output Pattern B)
| Code | What it Means | Severity |
|---|---|---|
| E9 | Indoor/outdoor unit communication error | High |
| UP | Compressor overcurrent interruption | High |
| U3, U4 | Open or short of outdoor unit thermistors | Medium |
| UF | Compressor overcurrent (compressor locked) | High |
| U2 | Abnormal high discharge temperature / insufficient refrigerant | High |
| U1, Ud | Abnormal high pressure / overheat protection | High |
| U5 | Abnormal temperature of heat sink | High |
| U8 | Outdoor unit fan protection stop | High |
| U6 | Compressor overcurrent / abnormal power module | High |
| U7 | Abnormal super heat (low discharge temperature) | High |
| U9, UH | Overvoltage / voltage shortage / current sensor error | High |
Indoor Unit Errors (P Codes)
P1: Intake Sensor Error
The thermistor reading air temperature at the indoor unit’s intake is faulty. Common causes: loose sensor connector, defective thermistor, or PCB sampling circuit fault. The unit may still cool but won’t modulate accurately based on room temperature. Cheap fix (parts under $80, repair from $130).
P2: Pipe (TH2) Sensor Error
The thermistor on the liquid pipe of the indoor heat exchanger is faulty. Same fix pattern as P1. Important sensor because it’s used to detect coil freezing.
P9: Pipe (TH5) Sensor Error
The thermistor on a different point of the indoor coil is faulty. Same fix pattern.
P4: Float Switch Connector Open / Drainage Issue
The drain pan’s float switch has detected a problem (either water buildup or a broken switch connection). One of the most common P codes we attend in Singapore. Causes: blocked drain pipe, failed drain pump (on cassette units), failed float switch, or loose connector. A proper drain pipe vacuum during servicing usually clears P4 immediately. See our water leak guide for the full breakdown.
P5: Drain Pump Error
The drain pump (on ceiling cassette and ducted indoor units) has failed. Replacement needed. Pump replacement runs $180 to $280 depending on model.
PA: Forced Compressor Error (Water Leakage)
The system has forced the compressor to stop because it detected an abnormal water leakage condition. Different from P4 (drainage backup). PA usually indicates something more serious, like the drainage system is fundamentally failing or water has reached electrical components. Switch off immediately.
P6: Freeze Protection / Overheat Protection
The indoor coil temperature is too low (cooling mode, freeze risk) or too high (heating mode, overheat risk). Most common cause we see in Singapore: dirty air filter restricting airflow across the coil. Other causes: low refrigerant, restricted airflow from blocked vents, or defective coil thermistor. Clean filters first. If P6 returns, coil cleaning or refrigerant diagnosis needed.
EE: Combination Error Between Indoor and Outdoor Unit
The indoor and outdoor units don’t match (excess connected indoor units, wrong capacity pairing, mismatched refrigerant types). Usually after a reinstallation or after one component has been replaced with the wrong model. Needs technician to verify system specs.
P8: Pipe Temperature Error
The pipe temperature is outside the expected range. Often related to refrigerant issues or restricted refrigerant flow. Diagnosis required.
PB (Pb): Indoor Unit Fan Motor Error
The indoor fan motor isn’t running or isn’t responding correctly. Causes: broken motor wiring, defective motor, failed indoor PCB, or mechanical blockage in the fan wheel. Fan motor replacement runs $200 to $350.
FB (Fb): Indoor Unit Control System Error
The indoor unit’s control system has a memory or PCB-level fault. Usually requires PCB replacement. $250 to $450.
PL: Refrigerant Circuit Abnormal
The refrigerant circuit has an abnormality. Possible causes: low refrigerant (slow leak), clogged expansion valve, restricted piping, or pressure sensor fault. Pressure test required.
Communication Errors (E Codes)
E0, E3: Remote Controller Transmission Error
The remote controller can’t transmit signals to the indoor unit. Common causes: weak remote batteries, line-of-sight issues, or failed remote. Try fresh batteries first. If still failing, the remote may need replacement.
E1, E2: Remote Controller Control Board Error
The remote controller’s own PCB has a fault. The remote itself needs replacement.
E4, E5: Communication Error Between Wired Remote and Indoor Unit
For installations using wired remotes (cassettes, ducted units). The wired remote and indoor PCB can’t communicate. Common causes: loose remote cable, damaged cable, defective remote, or defective indoor PCB. Check cable connections first.
E6, E7: Indoor/Outdoor Unit Communication Error
One of the most common Mitsubishi codes we attend in Singapore. The indoor and outdoor units can’t communicate. First check: is the outdoor unit isolator switched on? Common causes: tripped outdoor breaker, loose terminal connection on the communication cable, damaged transmission wire, or failed PCB on either end. We often find this is solved by re-tightening a loose terminal screw.
E9: Indoor/Outdoor Communication Error (Detected at Outdoor)
Same fault as E6/E7 but reported from the outdoor side. Same diagnosis pattern.
Outdoor Unit Errors (U Codes)
U1, Ud: Abnormal High Pressure / Overheat Protection (63H Activated)
The high pressure protection switch (63H) has tripped. Most common cause we see in Singapore: dirty outdoor condenser restricting heat dissipation. Other causes: refrigerant overcharge, blocked refrigerant piping, defective high pressure switch. Clean the outdoor unit first. If U1 persists after cleaning, refrigerant or pressure switch diagnosis needed.
U2: Abnormal High Discharge Temperature / 49C Activated / Insufficient Refrigerant
The compressor discharge temperature has exceeded safe limits, or the 49C protection has fired. Most often this means low refrigerant (the compressor running with insufficient gas overheats). Other causes: clogged expansion valve, restricted piping. Pressure test required.
U3, U4: Open / Short of Outdoor Unit Thermistors
One or more outdoor thermistors have an open or short circuit. Causes: damaged sensor wire, failed thermistor, or PCB sampling circuit fault. Cheap fix once the faulty sensor is identified.
U5: Abnormal Temperature of Heat Sink
The heat sink on the outdoor unit’s PCB is overheating. Causes: poor airflow around the outdoor unit (mounted too close to a wall), dust caked on the heat sink, failed cooling fan inside the control box, or excessive ambient temperature. In Singapore HDB flats, U5 sometimes appears because of poorly planned outdoor unit placement.
U6: Compressor Overcurrent / Abnormal Power Module
The compressor is drawing too much current, or the inverter power module has detected a fault. Serious electrical issue. Causes: compressor wear, refrigerant overcharge, failed power transistor, defective compressor capacitor (on non-inverter models). Don’t keep running the unit.
U7: Abnormal Super Heat / Low Discharge Temperature
The system has detected abnormal superheat (refrigerant not fully evaporating) or the discharge temperature is unusually low. Often indicates expansion valve failure or refrigerant overcharge.
U8: Outdoor Unit Fan Protection Stop
The outdoor fan motor has stopped due to protection logic. Causes: mechanical blockage (debris in the fan), failed fan motor, or fan capacitor failure. In Singapore we sometimes find leaves, plastic bags, or even small birds caught in outdoor fans. Visual inspection first.
U9, UH: Overvoltage / Voltage Shortage / Current Sensor Error
The system detected abnormal supply voltage or a current sensor fault. Singapore’s normal supply is 230V. If voltage is consistently out of range, electrician verification needed. Sometimes the current sensor on the PCB has failed and needs replacement.
UP: Compressor Overcurrent Interruption
The compressor’s overcurrent protection has interrupted operation. Similar root causes to U6 (compressor wear, refrigerant issues, power problems).
UF: Compressor Overcurrent (Compressor Locked)
The compressor has mechanically seized (locked rotor). Compressor needs replacement in most cases. $750+.
City Multi Commercial Quick Reference (For Office and Shop Installations)
City Multi systems (used in offices, F&B premises, and large commercial spaces in Singapore) use 4-digit fault codes. Common codes:
| Code | What it Means | Severity |
|---|---|---|
| 1102 (1202) | Discharge temperature fault | High |
| 1301 | Low pressure fault | High |
| 1302 (1402) | High pressure fault | High |
| 1500 (1600) | Refrigerant overcharge | High |
| 2502 | Drain pump fault | Medium |
| 4220 (4320) | Abnormal bus voltage drop | High |
| 4225 (4325) | Abnormal bus voltage rise | High |
| 4226 (4326) | Logic error / control power-supply fault | High |
| 4230 (4330) | Heatsink overheat protection | High |
| 4240 (4340) | Overload protection | High |
Codes in brackets are preliminary error codes. They indicate a precursor condition before the main fault triggers. Both should be investigated.
If you have a City Multi system showing any of these codes, contact us directly. Commercial diagnostics require specialised tools and we have technicians trained on City Multi systems specifically.
What to Do When You See a Mitsubishi Error Code
- Note the exact code or LED flash count. For wireless remotes, count flashes carefully (1 flash equals different code from 2 flashes).
- Check the severity using the tables above.
- For Medium severity codes (sensor faults, communication issues): book a service within the next few days.
- For High severity codes (especially U1, U2, U6, UF, PA): switch the aircon off and call a technician. Compressor damage risk if you continue.
- For P4 (drainage): stop using the unit until cleared, otherwise water may overflow inside your home.
- For E6/E7/E9 (communication): first verify the outdoor unit power and check the terminal connections on both ends of the communication cable.
- WhatsApp +65 8818 5781 with a photo of the code or video of the LED flash pattern. We can usually identify the cause before sending a team.
How Much Does Fixing a Mitsubishi Error Code Cost in Singapore?
Lion City Aircon pricing across Singapore (HDB, condo, landed, same rate):
- Diagnostic visit: $35 to $50 per unit
- Drain pipe vacuum (P4): from $90 per unit
- Chemical wash (for P6 from dirty coils): from $90 per unit
- Thermistor replacement (P1, P2, P9, U3, U4): from $130 (parts and labour)
- Drain pump replacement (P5): $180 to $280
- Capacitor replacement: from $130
- Fan motor replacement (PB, U8): $200 to $350
- Indoor PCB replacement (FB): $250 to $450
- Outdoor PCB replacement (E1, U5): $300 to $600
- Gas leak repair + recharge (U2, PL): from $180
- Compressor replacement (U6, UF): from $750
- Expansion valve replacement (U7): $300 to $500
If you’re on our annual maintenance contract, diagnostic visits are free and most thermistor, capacitor, and drainage fixes are included between scheduled visits.
Frequently Asked Questions About Mitsubishi Error Codes
What’s the most common Mitsubishi error code in Singapore?
E6/E7 (indoor-outdoor communication) is the most common, followed by P4 (drainage) and U1 (high pressure from dirty outdoor unit). All three are diagnosable in a single visit.
What’s the difference between Mr.Slim, Starmex, and City Multi?
They’re all Mitsubishi product lines. Starmex is Mitsubishi Electric’s residential line for Singapore (most HDB and condo installations). Mr.Slim is a broader Mitsubishi Heavy Industries and Electric range that includes residential and light commercial. City Multi is Mitsubishi’s commercial VRF lineup (offices, F&B, large commercial). Starmex and Mr.Slim residential models share the P/E/U code system. City Multi uses 4-digit codes.
How do I count the LED flashes on my Mitsubishi indoor unit?
The OPERATION INDICATOR lamp flashes a number of times, then pauses for about 2.5 seconds, then repeats. Count the flashes between pauses. Reference the wireless flash count column in the table above. The indoor unit also beeps the same number of times if a beeper is connected.
Can I clear a Mitsubishi error code by switching off the aircon?
Communication errors (E codes) sometimes clear with a full power reset if the cause was a transient power dip. Sensor and mechanical codes won’t clear because the underlying issue is physical. Compressor protection codes (U1, U2, U6) need the root cause fixed before they’ll clear.
Why does P4 keep coming back even after a service?
P4 (drainage) returning shortly after a service usually means the drain pipe wasn’t fully cleared, the drain pump is failing intermittently, or the slope of the pipe is wrong (water doesn’t flow downhill properly). Get a quality drainage check, not just a quick filter clean.
Should I try to fix Mitsubishi codes myself?
Filter cleaning, drain pipe checks, basic power resets, and visual inspection of cable connections are safe. Anything involving refrigerant (U1, U2, PL), inverter components (U5, U6), or PCB replacement needs a licensed technician. Refrigerant handling is regulated in Singapore.
How long does fixing a Mitsubishi error code take?
Most diagnoses take 30 to 45 minutes. Sensor replacements add 30 minutes. PCB or fan motor replacements take 60 to 90 minutes. Compressor replacement takes 2 to 3 hours. We carry common parts on the truck, so most fixes are complete in a single visit.
Will running my Mitsubishi with an error code damage it?
Depends on the severity. Medium severity codes (P1, P2, E0) won’t cause additional damage short-term. High severity codes (U1, U2, U6, UF, PA, PB) can cause expensive component damage. When in doubt, switch off and ask us.
What’s the difference between Mitsubishi Electric (Starmex) and Mitsubishi Heavy Industries?
They’re separate companies that both manufacture aircons. Mitsubishi Electric makes Starmex (the most popular residential brand in Singapore). Mitsubishi Heavy Industries makes a different product line. Both use similar code systems but with some model-specific variations. The codes covered above apply to both for the most common faults.
Get Your Mitsubishi Aircon Fixed Today
Most Mitsubishi error codes are diagnosable in a single visit. The longer you wait with an active fault, the more likely cascading damage develops, especially with U-series codes affecting the compressor or inverter.
WhatsApp +65 8818 5781 with a photo of the error code or a video of the LED flash pattern. We diagnose remotely where possible and dispatch a team. Same-day service in most cases across Singapore. 22,000+ jobs done since 2016, 5.0★ across 1,500+ Google reviews, BizSafe Level 3 certified.
No scare tactics. No upselling. If your fix is a $130 thermistor, we’ll tell you that and price it accordingly. If it’s a serious inverter or compressor issue, we’ll show you what we found and give you honest repair-versus-replace numbers before doing anything.
WhatsApp Lion City Aircon · Call +65 8818 5781 · Book online
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