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 blade. Signal voltage will vary from about 0.29 at idle to about 4.8 volts at wide open throttle. 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 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:

^ No Code 33 or Code 34
^ Engine is running.
^ Air Flow less than 17 gm/sec.
^ TPS voltage greater than 4.3 volts.
^ Above conditions exist for over 1.25 seconds.

OR

With throttle closed, the TPS should read less than 0.98 volts. If it doesn't, make sure cruise control and throttle cables are not being held open.

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

3. Probing CKT 808 with a test light checks the 5 volt return circuit. A faulty sensor ground circuit will cause a Code 21.


DIAGNOSTIC AIDS:

^ A "Scan" tool reads throttle position in volts. 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 808 will result in a Code 21. Codes 15 and 21 are stored at the same time could be the result of an open CKT 808 which would also turn the temperature warning indicator "ON". "Scan" TPS while depressing accelerator pedal with engine stopped and ignition "ON". Display should vary from below 2500 mV (2.5 volts) when throttle was closed, to over 4500 mV (4.5 volts) when throttle is held at wide open throttle position. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.