DTC 21

Code 21 Chart:

Throttle Position Sensor Circuit Wiring Diagram:

CIRCUIT DESCRIPTION:


The throttle position sensor (TPS) provides a voltage signal that changes relative to the throttle opening. Signal voltage will vary from about 0.5 volt at idle to about 5 volt 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:

^ Engine is running
^ No Code 33 or 34
^ MAP less than 65 kPa
^ TPS signal voltage greater than approximately 4.0 volts (78%)
^ Above conditions exist for over 5 seconds.

OR

^ TPS voltage greater than 4.7 volts. With throttle closed the TPS should read less than 0.9 volt. If it doesn't, check adjustment.

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

3. Probing CKT 452 with a test light checks the TPS ground circuit because an open or very high resistance ground circuit will cause a Code 21.


DIAGNOSTIC AIDS:


^ A "Scan" tool displays throttle position in volts. It should display 0.400 volt TO 0.900 volts with throttle closed and ignition "ON" or at idle. Voltage should increase at a steady rate as throttle is moved toward wide open throttle (WOT).

^ Also some "Scan" tools will display throttle angle. 0% = closed throttle 100% = WOT.

^ An open in CKT 452 will result in a Code 21.

^ Codes 15, 21 and 66 stored at the same time could be the result of an open CKT 452. "Scan" TPS while depressing accelerator pedal with engine stopped and ignition "ON". Display should vary from below 500 mV (0.5 volts) when throttle is closed, to over 4500 mV (4.5 volts) when throttle is held wide open.

^ Check condition of connector and sensor terminals for corrosion, and clean or replace as necessary. If corrosion found, check condition of connector seal, repair and/or replace if necessary.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.