Code 21B: TPS Circuit (Signal Volt Low): Notes

Throttle Position Sensor (TPS) provides a voltage signal which changes relative to throttle opening. Signal voltage varies from less than .9 volt at idle to approximately 4.5 volts at wide open throttle. The TPS signal is used by ECM for fuel control and most ECM controlled outputs.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This determines if Code 21B is from a hard failure or an intermittent condition. Code 21B will set if engine is running and TPS reading is less than .2 volt (200 mV).
This step simulates conditions for a Code 21A. If Code 21A is set, or Scan tester displays over 4 volts, ECM and wiring are okay.
Scan tester may not display 12 volts, but ECM recognizes the voltage as over 4 volts, indicating that circuit No. 417 and ECM are okay.
If circuit No. 416 is open or shorted to ground, a Code 33B may also be stored.