Whirlpool Dryer Error Code 4

Error code 4 on a Whirlpool dryer indicates a possible motor transistor fault, detected during the startup sequence. The machine control board monitors the motor transistor, which is responsible for switching power to the drive motor. When the control board detects that the transistor appears either open (no conductivity where expected) or shorted (conductivity where there should be none), it triggers this error to prevent potential damage to the motor circuit or related components.

The motor transistor is an integral part of the control board's drive circuitry. A shorted transistor can allow uncontrolled current flow to the motor, while an open transistor prevents the motor from receiving power at all. Both conditions are flagged during startup diagnostics because the control board performs a self-check of the relay and transistor states before allowing the dryer to run.

Diagnosis begins by checking for loose or corroded connections throughout the motor circuit, since poor contact can mimic a transistor fault. Running the System Check Mode is the critical next step: if the motor relay functions correctly during this test, the error code can be disregarded as a transient fault. If the relay fails to function, the machine control board itself is the likely culprit and will need to be replaced, as the transistor is integrated into the board rather than being a separately serviceable component.