Part 2 of 2

CODE 21 THROTTLE POSITION SENSOR (TPS) CIRCUIT

Code Chart 21B:

TPS Circuit:

CIRCUIT DESCRIPTION:

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle valve position. Signal voltage will vary from less than 1.25 volts at idle to about 5.0 volts at wide open throttle (WOT). The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs.

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

1. This step checks to see if Code 21B is the result of a hard failure or an intermittent conidition.

Code 21 will set if:

^ Engine is running.
^ TPS voltage is below 0.2 volt (200 mV).

2. This step simulates conditions for a Code 21A. If a Code 21A is set, or the Scan tool displays over 4 volts, the ECM and wiring are OK.

3. The Scan tool may not display 12 volts. The important thing is that the ECM recognizes the voltage as over 4 volts, indicating that the PPL/RED wire and the ECM are OK.

4. If PPL/ORN wire is open or shorted to ground, there may also be a stored Code 33.

DIAGNOSTIC AIDS:

A Scan tool displays throttle position in volts. Closed throttle voltage should be less than 1.25 volts. TPS voltage should increase at a steady rate as throttle is moved to WOT. A Code 21B will result if BLK/WHT wire is open or PPL/RED wire is shorted to voltage. If Code 21B is intermittent, Testing and Inspection