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 0.4 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 controlled 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.
^ Code 33 or 34 not present at first start up.
^ All conditions met for 5 seconds.

With throttle closed ignition "ON", or at idle, the TPS voltage should be 0.40 volt +/- .05 volt. If it doesn't check adjustment.

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 to 12 volts, checks the sensor ground CKT 452. A faulty sensor ground circuit will cause a Code 21.

DIAGNOSTIC AIDS:

^ A "Scan" tool reads throttle position in volts. It should read 0.40V +/- .05V with throttle closed and ignition on or at idle. Voltage should increase at a steady rate as throttle is moved toward WOT. Also some "Scan" tools will read throttle blade 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.

Check For:

^ Poor connection or damaged harness. Inspect ECM harness connectors for backed out terminal "C13" or "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent test. If connections and harness check OK, monitor TPS voltage display while moving related connectors and wiring harness. If the failure is induced, the TPS voltage display will change. This may help to isolate the location of the malfunction.

^ TPS scaling. Observe TPS voltage display while depressing accelerator pedal with engine stopped and ignition "ON". Display should vary from closed throttle TPS voltage when throttle was closed, to over 4.5 volts (4500 mV) when throttle is held at wide open throttle position.