Powertrain Controls - ECM/PCM

Code 21 Chart:

Code 21 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Throttle Position Sensor (TPS) provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about 0.5 at idle to about 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 control 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. Code 21 will set if:

- TPS signal voltage is greater than 2.5 volts
- Engine is running
- Air flow is less than 15 gm/sec.
- All conditions met for 3 seconds.
OR
- TPS signal voltage over 4.9 volts with ignition "ON".
- With throttle closed the TPS should read less than 0.96 volt. If it doesn't replace sensor.

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

3. Probing CKT 452 with a test light checks the sensor ground circuit 452. A faulty sensor ground will cause a Code 21.

DIAGNOSTIC AIDS:

A "Scan" tool reads throttle position in volts. Should read 0.96 volts with throttle closed and ignition on or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. An open in CKT 452 will result in a Code 21, Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.