Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
- 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.
- 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.
- 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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.