Whirlpool Microwave Error Code Err4

Err4 indicates that the ambient temperature sensor is reading a value outside the allowed range. This code is displayed during the diagnostic test mode when the Defrost key is pressed. It typically points to a failed thermistor, a wiring connection problem, or in some cases an actual temperature extreme in the installation environment.

Err4 surfaces during diagnostic test mode rather than during standard cooking, so the microwave may still operate normally for basic use. However, a faulty temperature sensor means the unit cannot properly monitor its thermal environment, which could mask overheating conditions. It is advisable to have the fault diagnosed and corrected before continued regular use.

Repair costs vary depending on the faulty component. A replacement thermistor is generally an inexpensive part, typically in the range of $10 to $40 for the component alone. If the control board is the cause, parts can range from $80 to $200 or more. Adding professional labor costs typically brings the total service call to somewhere between $100 and $300 depending on your location and the parts required.

A knowledgeable DIYer can check and reseat wiring harness connections without specialized tools. Testing the thermistor with a multimeter is also achievable at home. However, replacing the thermistor or control board involves working near high-voltage components, so the microwave must be fully unplugged and the capacitor discharged before any internal inspection.

A power reset by unplugging the unit for a few minutes may temporarily clear the code, but if the underlying cause is a defective thermistor or wiring fault, the error will return when the diagnostic test is run again. A reset does not repair the hardware problem responsible for the fault.