Powertrain Controls - ECM/PCM

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 0.5 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. TPS reading is greater than 2.5 volts
b. MAP reading below 52 kPa (7.5 psi).
c. All the above conditions are present for at least eight seconds.

2. With the TPS sensor disconnected, the TPS voltage should go low if the ECM and wiring are OK.

3. Probing circuit 452 with a test light checks the five volt return circuit. A faulty five volt return will cause a Code 21.


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 with the ignition "ON" or engine idling.
2. A Code 21 will result if circuit 452 is open. If a Code 21 is intermittent, see DIAGNOSIS BY SYMPTOM.