Powertrain Controls - ECM/PCM

DTC 21 Throttle Position Sensor (Signal Voltage High):

Throttle Position Sensor Wiring Diagram:

Circuit Description:

The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle blade. Signal voltage will vary from about 0.5 at idle to about 4.8 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the ECM for fuel control and for many of the ECM control outputs.


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

1. DTC 21 will set if:

^ No DTC 33 or DTC 34.
^ Engine is running and RPM greater than 600.
^ TP sensor signal voltage is greater than 3.82 volts.
^ All conditions met for 10 seconds.

OR

^ With throttle closed, the TP sensor should read less than 0.98 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 ECM and wiring are OK.

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

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
Throttle Angle 100% = WOT.

An open in CKT 470 will result in a DTC 21.

DTCs 15 and 21 stored at the same time could be the result of an open CKT 470 which would also turn the temperature warning indicator "ON." Scan the TP sensor while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from about 0.5 volt when throttle was closed, to about 4.8 volts when throttle is held at Wide Open Throttle (WOT) position.

- Intermittent Malfunctions