Code 21A, 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 21A is from a hard failure or an intermittent condition. Code 21A sets if TPS reading is greater than 2.5 volts, if engine speed is less than 1800 RPM of if MAP reading is less than 60 kPa and if all these conditions are present for 2 seconds.
2. This step simulates conditions for a Code 21B. If the ECM recognizes the change, the ECM and the Purple/Red wire and the Purple/Orange wire are okay.
3. This isolates a faulty sensor, ECM or an open in circuit D2 (Black/White wire). If Black/White wire is open, Code 23A may also be present.