Powertrain Controls - ECM/PCM

Code Chart 21:

CHART 1 OF 2

DTC 21 Throttle Position Sensor Circuit (Signal Voltage High/Low):

CHART 2 OF 2

Throttle Position Sensor Wiring Circuit:

Circuit Description:
The Throttle Position (TP) sensor provides a voltage signal that changes relative to the throttle valve. Signal voltage will vary from .33 to 1.33 volts at idle to about 4.5 volts at Wide Open Throttle (WOT).

The TP sensor signal is one of the most important inputs used by the Engine Control Module (ECM) for fuel control and for many of the ECM controlled outputs.

DTC 21 Will Set When:
^ Engine running under 1750 RPM.
^ TP sensor less than .2 volt or greater than 4.8 volts.
^ MAP reading below 65 kPa.
^ All of the above conditions present for 5 seconds.

Action Taken (ECM will default to): Malfunction indicator Lamp (MIL) illuminates. ECM will substitute a fixed value for throttle position.

DTC Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. The TP sensor has a auto zeroing feature. If the voltage reading is within the range of about 33 to 1.33 volts, the ECM will use that value as closed throttle. If the voltage reading is outside of the auto zero range at closed throttle. check for a binding throttle cable or damaged linkage. If OK. continue with diagnostics.
2. If the ECM recognizes the change of state, the ECM, CKT 474, and CKT 417 are OK.
3. This step isolates a faulty sensor, ECM, or an open CKT 452. If CKT 452 is open, there may also be other diagnostic trouble codes set.
4. This step checks to see if DTC 21 is the result of a hard failure or an intermittent condition.
5. This step simulates conditions for a DTC 21 to set. If the scan tool displays over 4 volts, the ECM and wiring are OK.
6. This simulates a high signal voltage to check for an open or short in CKT 417. The scan tool should read over 4 volts.
7. With the ignition "ON" (or at idle) and the throttle closed, voltage at ECM terminal "B12" should be .33 to 1.33 volts. If not, replace the TP sensor.
8. If CKT 474 is shorted to ground or sensor ground, there also may be other DTC(s) stored.

Diagnostic Aids:
A scan tool displays throttle position in volts. The voltage at closed throttle should be .33 to 1.33 volts. TP sensor voltage should increase at a steady rate as throttle is moved slowly to Wide Open Throttle (WOT) position.

If DTC 21 is intermittent, refer to "Diagnosis By Symptoms." - Intermittent Malfunctions