Whirlpool Microwave Error Code MV-4903

MV-4903 means the microwave relay identified as 4903 on the Appliance Control Unit has experienced a welded contact condition. This means the relay switch is stuck in the closed position and can no longer open to cut power to the microwave circuit. It is a hardware failure that requires physical inspection and likely component replacement.

No, the microwave should not be used while MV-4903 is active. A welded relay contact can cause the magnetron to energize unintentionally, creating a serious safety hazard. Disconnect power to the unit and do not operate it until the relay and related components have been inspected and repaired.

Repair costs for MV-4903 vary depending on whether just the relay, the full ACU, or additional components like the magnetron need replacement. Parts and labor for an ACU replacement typically range from $150 to $350 or more depending on the specific model and service rates in your area. If the magnetron is also found to be faulty, costs will increase. In some cases, replacement of an older unit may be more economical than repair.

Resetting the microwave by unplugging it will not clear MV-4903 if the relay contact is physically welded closed. The error reflects an actual mechanical failure of the relay component, not a software glitch. The underlying hardware issue must be corrected before the error will clear and the unit will operate normally.

Start by unplugging the microwave or disconnecting power at the breaker. Inspect the wiring harness connected to relay 4903 on the ACU for loose or corroded connections. Check whether the relay contacts are physically welded closed by testing continuity across the contacts. If the relay is confirmed faulty, the relay itself or the ACU assembly will need to be replaced by a qualified technician.