The Throttle Position sensor is potentiometer. A 5 volt reference is provided on CKT 605 and ground is provided on CKT 808. The TP sensor signal CKT 417 varies between ground and 5 volts based on the position of the throttle plates. At low throttle angle, the TP sensor signal voltage is low. The PCM uses TP sensor information to determine idle, Wide Open Throttle (WOT), deceleration enleanment and acceleration enrichment. This diagnostic test is designed to determine when the throttle position sensor reading is too high out of its estimated range for its current operating engine speed. The PCM does this by monitoring changes in TP sensor within a certain period of time. If the change is 0.6 degrees or less within 0.1 second, the PCM compares the current throttle position with a stored throttle position that is considered acceptable for the current engine speed. If the current throttle position is greater than the stored value the TP sensor is considered stuck and DTC P0121 will set.

The throttle position sensor input is not within its expected range.

PCM disables the torque converter clutch.

Number(s) below refer to the step number(s) on the Diagnostic Table.

3. Observe the TP Sensor display voltage for a condition in which the TP Sensor is rotated but the TP Sensor display voltage stays steady. This stuck condition could occur anywhere in the TP sensors range. Perform this check several times. If the TP Sensor display matches the TP sensor rotation then perform the MAP sensor diagnosis since the expected TP sensor reading is based on the MAP sensor input.