With PFI

Code 21 Chart:

Code 21 Wiring Diagram:

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.


NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.


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 intermittant 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 below 1300 rpm
^ All of the above conditions are present for 10 seconds

2. This simulates conditions for a code 22. If the ECM recognizes the change of state, the ECM and CKT's 416 and 417 are OK.

3. This isolates a faulty sensor, ECM or an open CKT 470.


DIAGNOSTIC AIDS:

^ A "Scan" tool reads throttle position in volts. Closed throttle voltage should be less than 1.0 volt. TPS voltage should increase at a steady rate as the 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 intermittant, Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.