Part 2 of 2

Code Chart 21:

TPS Circuit:

CIRCUIT DESCRIPTION:
The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle valve. Signal voltage will vary from about 0.33 to 1.33 volts at idle to about 4.5 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 controlled outputs.

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

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

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

3. This simulates a high signal voltage to check for an open or short in CKT 417. The Scan tool will not read battery voltage, but the ECM should recognize the signal on CKT 417.

4. See Service and Repair for TPS replacement procedures.

DIAGNOSTIC AIDS:
A "Scan" tool displays TPS in volts. Closed throttle voltage should be between 0.30 to 1.33 volts, and the voltage value should increase at a steady rate as the throttle is opened. If a Code 21 is intermittent, Testing and Inspection