Powertrain Controls - ECM/PCM

Code 21 Chart:

Throttle Position Sensor (TPS) 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 0.29 at idle to about 4.8 volts at Wide Open Throttle (WOT). The TPS signal is one of the most important inputs used by the Electronic Control Module (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 SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION 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:

- Engine is running.
- TPS signal voltage is greater than 3.8 volts.
- Air flow is less than 17 gm/sec.
- All conditions met for 10 seconds.

OR

- TPS check: The TPS has an auto zeroing feature. If the voltage reading is within the range of 0.29 to 0.98 volt, the ECM will use that value as closed throttle. If the voltage reading is out of the auto zero range on an existing or replacement TPS, make sure the cruise control and throttle cables are not being held open. If ok replace TPS 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 5 volts return CKT, because a faulty 5 volts return will cause a Code 21.


DIAGNOSTIC AIDS:

A "Scan" tool reads throttle position in volts. Should read. Voltage should increase at a steady rate as throttle is moved toward WOT. Also some "Scan" tools will read throttle angle .0% = closed throttle 100% = WOT. An open in CKT 452 will result in a Code 21. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.