With TBI

Code 21 Chart:

Wiring Diagram For TPS:

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 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 controlled outputs.


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

1. This checks to see if a Code 21 is the result of a hard code failure or an intermittent problem.
A Code 21 will set under the following conditions:
a. Engine speed less than 1800 rpm.
b. TPS reading is greater than 2.5 volts
c. MAP reading below 55 kPa (8.0 psi).
d. All the above conditions are present for at least two seconds.

2. This simulates conditions for a Code 22. If the ECM recognizes the change of state, the ECM and circuits 416 and 417 are OK.

3. This step isolates a faulty sensor, ECM, or an open circuit 452. If circuit 452 is open, there may also be a Code 15 stored.


DIAGNOSTIC AIDS:

1. A "Scan" tool displays TPS in volts. Closed throttle voltage should be less than 1.25 volts, and the voltage value should increase at a steady rate as the throttle is opened.
2. A Code 21 will result if circuit 452 is open or circuit 417 is shorted to voltage. If a Code 21 is intermittent, see DIAGNOSIS BY SYMPTOM.