Mitsubishi Error Code E9: Indoor/Outdoor Communication Fault
Warning: Your Mitsubishi HVAC system has encountered a communication issue between the indoor and outdoor units. It's safe to operate, but you should schedule a professional repair soon.
LED Blink Pattern
How to Fix Mitsubishi Code E9
- Step 1: Turn off your HVAC system at the thermostat and the main power switch.
- Step 2: Check for any visible damage to the communication cable or control boards. If you find any, do not attempt to repair or replace them yourself.
- Step 3: Contact a professional HVAC technician to diagnose and repair the issue.
How to Reset Mitsubishi Code E9
- Turn off the unit using the remote control or wall controller.
- Turn off the circuit breaker for the outdoor and indoor units. Wait 60 seconds.
- Restore power at the breaker.
- Turn the unit on with the remote control. If the error returns, the fault needs professional diagnosis.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Mitsubishi Error Code E9 Mean?
The E9 error on your Mitsubishi HVAC system indicates a communication fault between the indoor and outdoor units. This could be due to a broken wire, a faulty control board, or an issue with the communication cable. The system will continue to operate, but you may notice reduced performance or comfort. It's important to address this issue promptly to prevent further damage or system failure.
Common Causes
- Damaged or broken communication cable between indoor and outdoor units
- Faulty control board in either the indoor or outdoor unit
- Interference from other electronic devices or power surges
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| You see a broken or damaged communication cable | Inspect the cable for any visible damage or breaks. Use a multimeter to test for continuity. | Continuity with no visible damage |
| You suspect a faulty control board | Use a multimeter to test for voltage at the control board. Also, check for any visible signs of damage or overheating. | Voltage present with no visible damage or overheating |
Applicable Mitsubishi Models
- City Multi (VRF)(electric)
- City Multi (Y)(electric)
- Diamond (PJ)(electric)
- Diamond Plus(electric)
- Diamond Series(electric)
- Ducted Systems(electric)
- M-Series(electric)
- MSZ(electric)
- MSZ Series(electric)
- MSZ-AP(electric)
- MSZ-AP Series(electric)
- MSZ-AP5 Series(electric)
- MSZ-AS(electric)
- MSZ-FD(electric)
- MSZ-FE(electric)
- MSZ-FS(electric)
- MSZ-FS/FD Series(electric)
- MSZ-FT(electric)
- MSZ-FY(electric)
- MSZ-GE(electric)
- MSZ-LV(electric)
- MUZ-FE Series(electric)
- P-Series(electric)
- PUMA(electric)
- PUMY(electric)
- Puff (P-Series)(electric)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Communication Cable | 503975-0000 | — | Find Part |
| Indoor Control Board | 503976-0000 | — | Find Part |
| Outdoor Control Board | 503977-0000 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Mitsubishi model families as E9.
| Code | Description | Severity |
|---|---|---|
| 1 | Indoor/Outdoor Mismatch | Warning |
| 2 | Power Supply Phase Error | Warning |
| 3 | Communication Error | Warning |
| 4 | Inverter Error | Warning |
| 5 | Outdoor Thermistor Open/Short | Warning |
| 6 | Indoor Freeze/Overheat | Warning |
| 7 | Outdoor Freeze/Overheat | Warning |
| E6 | Indoor/Outdoor Communication Error | Warning |
| P1 | Intake Sensor Error | Warning |
| P2 | Indoor Pipe Thermistor Error | Warning |