Mitsubishi Air Conditioner Error Code Er4

Er4 is a mode designation error indicating that a parameter write was attempted while the command source was not set to the operation panel. The unit requires PU operation mode to be active before it will accept parameter changes from the panel. This is a configuration issue, not a hardware failure. Checking the operation mode and verifying the Pr.551 setting are the first steps to resolve it.

No, Er4 is not a safety-critical error. It does not indicate a refrigerant leak, electrical fault, or mechanical failure. The unit is simply refusing to accept a parameter change because the wrong command source mode is active. The system is functioning as intended by protecting parameter integrity.

Because Er4 is a configuration error rather than a parts failure, the cost is typically limited to the labor time needed to access and correct the parameter settings. If a technician is called out specifically for this issue, expect to pay somewhere in the range of $75 to $200 depending on your region and the service provider. No replacement components should be required in the vast majority of cases.

Start by confirming that the unit is set to PU operation mode. Next, check the Pr.551 parameter setting to ensure the command source is correctly designated as the operation panel. If an external controller or communication device is connected and actively commanding the unit, that source must be disabled or disconnected before panel writes are allowed. No replacement parts should be needed for this fix in most cases.

A simple reset may temporarily clear the error display, but Er4 will return if the underlying mode configuration is not corrected. The root cause is a mismatch between the active command source and the attempted parameter write operation. Correcting the operation mode and Pr.551 setting is required for a lasting resolution.