Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle valve. Signal voltage will vary from less than 1.0 volt at idle to about 4.6 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 many of the ECM controlled outputs.

TEST DESCRIPTION
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.
A Code 21 will set if:
^ TPS reading above 2.5 volts.
^ MAP reading below 70 kPa (M/T) or 81 kPa (A/T).
^ Engine speed less than 1300 rpm.
^ All of the above conditions are present for 10 seconds.
2. This step simulates conditions for a Code 22. If the ECM recognizes the change of state, the ECM and CKTs 416 and 417 are OK.
3. This step isolates a faulty sensor, ECM, or an open CKT 155.

DIAGNOSTIC AIDS
A "Scan" tool displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt. TPS voltage should increase at a steady rate as throttle is moved to WOT.

A Code 21 will result if CKT 155 is open or CKT 417 is shorted to voltage. If Code 21 is intermittent, refer to Symptoms. Testing and Inspection