Powertrain Controls - ECM/PCM

Diagnostic Chart:

TP Sensor Electrical Schematic:

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor has a potentiometer whose resistance changes along with the throttle valve position. The Engine Control Module (ECM) provides a 5 volt reference to the TP sensor. The ECM reads the voltage across the sensor and converts it into throttle position. When the TP sensor resistance decreases, indicating the throttle valve opening is increasing to wide open throttle, the voltage being monitored at the ECM increases. When the TP sensor resistances increases, indicating the throttle valve opening is decreasing to idle, the voltage being monitored as the ECM decreases.

Diagnostic Trouble Code (DTC) 21 will set if the following condition is met for at least 1.6 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 voltage in LT GRN/WHT wire or for a faulty ECM.
2. Checks for an open or short to voltage in LT GRN wire or for a faulty ECM.
3. Checks for an open LT GRN/BLK wire or for a faulty ECM or a misadjusted or faulty TP sensor.

DIAGNOSTIC AIDS
Refer to Computer and Control Systems / Throttle Position Sensor / Adjustments for TP sensor adjustment procedure. Adjustments

DTC 21, DTC 22 and DTC 46 stored at the same time could be the result of an open LT GRN wire.

INTERMITTENT MALFUNCTIONS
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.