Whirlpool Dryer Error Code 91

Error code 91 on a Whirlpool dryer indicates a Lower Rotation Sensor Fault. The rotation sensor, sometimes called a drum rotation sensor or tachometer, monitors the movement of the dryer drum to confirm it is spinning at the correct speed during operation. When the control board detects that the signal from the lower rotation sensor is absent, erratic, or outside the expected parameters, it triggers this fault code and may halt the drying cycle to prevent damage to the motor or drum assembly.

The lower rotation sensor typically works by detecting pulses generated as the drum rotates, sending a frequency-based signal back to the main control board. A fault can occur when the sensor itself has failed internally, when the wiring harness connecting the sensor to the control board has become damaged or disconnected, or when the drum has stopped rotating due to a mechanical obstruction. Worn drum rollers, a broken drive belt, or a seized idler pulley can all prevent the drum from turning, which the control board interprets as a sensor fault even if the sensor itself is functional.

Diagnosing this code requires inspecting the sensor and its wiring for visible damage, verifying that the drum rotates freely by hand with the belt removed, and checking for continuity through the sensor circuit. The control board itself can also be a factor if it is failing to correctly read a signal that is otherwise present and valid.