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 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.
- 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).
- 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.
- 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.
- If Purple/Orange wire is open or shorted to ground, a Code 33 may also be stored.
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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.