Powertrain Controls - ECM/PCM

Code Chart 21:

Throttle Position Sensor Circuit:

CIRCUIT DESCRIPTION:

The Throttle Position Sensor (TPS) has a potentiometer whose resistance changes along with the throttle valve position. The ECM provides a 5.0 volt reference to the sensor. The ECM reads the voltage across the sensor and converts it into throttle position. When the sensor resistance decreases, indicating the throttle valve opening is increasing to wide open throttle, the voltage being monitored at the ECM increases. When the sensor resistances increases, indicating the throttle valve opening is decreasing to idle, the voltage being monitored as the ECM decreases. Code 21 will set if the following condition is met for at least 2 seconds; High voltage input at the ECM indicated with the engine running at idle.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks for an open or short to B+ in LT GRN/WHT wire or for a faulty ECM.

2. Checks for an open or short to B+ in LT GRN wire or for a faulty ECM.

3. Checks for a faulty ECM or a misadjusted or faulty throttle position sensor.

DIAGNOSTIC AIDS:

Codes 21 and 22 stored at the same time could be the result of an open LT GRN wire.