Code 21B Throttle Position (TP) Sensor Circuit

SIGNAL VOLTAGE LOW




Circuit Description
The Throttle Position (TP) Sensor provides a voltage signal that changes relative to the Throttle Body position. Signal voltage will vary from less than 1.0 volts at idle to about 5.0 volts at Wide Open Throttle.

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.




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

1. This checks to see if Diagnostic Trouble Code (DTC) 21B is the result of a hard failure or an intermittent condition. A DTC 21B will set if:
- The Engine is running.
- TP Sensor voltage is below 0.20 volts (200mV).

2. This step simulates conditions for a DTC 21A. If a DTC 21A is set, or the "Scan Tool" displays over 4 volts, the ECM and wiring are OK.
3. The "Scan Tool" may not display 12 volts. The important thing is that the ECM recognizes the voltage as over 4 volts, indicating that BLU/RED wire and the ECM are OK.
4. If the 5 volt reference wire is open or shorted to ground, there may also be a stored DTC 33B.

Diagnostic Aids
- A "Scan Tool" displays Throttle Position in volts. Closed Throttle voltage should be less than 1.0 volts. TP Sensor voltage should increase at a steady rate as Throttle is moved to Wide Open Throttle.
- An open or grounded BLU/ORG or BLU/RED wire will result in a DTC 21B. If DTC 21B is intermittent, refer to Diagnosis by Symptom. Symptom Related Diagnostic Procedures
- If an "OPEN" circuit occurs in the signal line on an Automatic Transmission Vehicle, the "Scan Tool" will indicate 2.5 volts but DTC 21 may not be logged in the ECM.