Code 21B, Throttle Position Sensor Circuit: Notes

Throttle Position Sensor (TPS) provides a voltage signal that changes relative to throttle opening. Signal voltage varies from less than 1.25 volt at idle to approximately 5.0 volts at wide open throttle. TPS signal is one of the most important inputs used by the ECM for fuel control and most ECM-controlled outputs.

1. This checks if Code 21B is from a hard failure or an intermittent condition. Code 21B sets if engine is running and TPS reading is less than .2 volt (200 mV).
2. This step simulates conditions for a Code 21A. If code 21B is set, or Scan tester displays more than 4 volts, the ECM and wiring are okay.
3. The Scan tester may not display 12 volts, but ECM recognizes the voltage as more than 4 volts, indicating the Purple/Red wire and ECM are okay.
4. If Purple/Orange wire is open or shorted to ground, a Code 33 may also be stored.