DTC 21

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 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 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:

^ Engine is running
^ TPS signal voltage is greater than 2.5 volts
^ Air flow is less than 12 gm/sec.
^ All conditions met for 5 seconds OR TPS signal voltage over 4.5 volts with ignition "ON".

The TPS has an auto zeroing feature. If the voltage reading is within the range of 0.35 to 0.7 volts, the ECM will use that value as closed throttle. If the voltage reading is out of auto zero range at closed throttle see TPS ADJUSTMENT under ADJUSTMENT PROCEDURES

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

3. Probing CKT 452 with a test light checks the 5V return CKT, because a faulty 5V return will cause a Code 21.

DIAGNOSTIC AIDS:

A "Scan" tool reads throttle position in volts. It should read 0.55V +/- .08V 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.