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 blade angle. 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: Numbers below refer to the 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 to set. 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 should read over 4 volts.

4. With the ignition "ON" or at idle and the throttle closed, voltage at ECM terminal "B12" should be .33 to 1.33 volts. If not, replace the TPS.

5. If CKT 474 is shorted to ground or sensor ground, there also may be other codes stored.

DIAGNOSTIC AIDS:

^ A "Scan" tool displays TPS in volts. Closed throttle voltage should be between 0.33 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