Powertrain Controls - ECM/PCM

DTC 21 Chart:

Throttle Position Sensor Circuit:

Circuit Description:
The Throttle Position (TP) sensor provides a voltage signal to the PCM that increases as the throttle blade angle increases. This signal voltage will vary from approximately .5 volt at idle to 4.8 volts at Wide Open Throttle (WOT). The TP sensor is one of the most important inputs to the PCM for governing fuel control of the engine.

DTC 21 Will Set When:
No DTC 33 or DTC 34, TP sensor voltage is greater than 3.8 volts, engine speed is above 600 RPM, both conditions met for 10 seconds under steady throttle, road load conditions, or with throttle closed, the TP sensor should read less than .98 volt. If it doesn't, make sure cruise control and throttle cables are not being held open.

Action Taken (PCM will default to):
The PCM will determine fuel and air calculations using calibrated values from a default table. The transmission will have maximum line pressure, no TCC and no 4th gear in hot mode. The MIL will become illuminated.

DTC 21 Will Clear When:
A current DTC 21 will clear when a high signal voltage above the calibrated threshold is no longer detected. A history DTC 21 will clear after 50 consecutive ignition key cycles without a current DTC 21 being stored.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. With throttle closed, the TP sensor should read less than .98 volt. If it doesn't, make sure cruise control and throttle cables are not being held open.

2. With the TP sensor disconnected, the TP sensor voltage should go low, if the PCM and wiring are OK.

3. Probing CKT 470 with a test light checks the 5 volt return circuit. A faulty sensor ground circuit will cause a DTC 21. DTC 33, 66 or 71 may also be set.

Diagnostic Aids:
A Tech 1 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 470 will result in a DTC 21.

Scan TP sensor while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from about .5 volt when throttle was closed, to about 4.8 volts when throttle is held at WOT position.

Refer to "Intermittents" in "Diagnosis By Symptom." - Intermittent Malfunctions