P0121 Toyota
The P0121 diagnostic trouble code (DTC) in a Toyota indicates an issue with the Throttle/Pedal Position Sensor “A” Circuit Range/Performance. This means that the Throttle Position Sensor (TPS) is sending an out-of-range or inconsistent signal to the Engine Control Module (ECM), potentially affecting throttle response and engine performance.
Common Symptoms of P0121 in Toyota Vehicles
- Check Engine Light (CEL) illuminated
- Poor acceleration or hesitation
- Engine stalling or rough idling
- Reduced power (limp mode)
- Unstable throttle response
Possible Causes
- Faulty Throttle Position Sensor (TPS) – The sensor may be damaged, sending incorrect voltage readings.
- Dirty or Sticking Throttle Body – Carbon buildup can cause irregular throttle movement.
- Faulty Accelerator Pedal Position Sensor (APP) – Some Toyota models use both TPS and APP sensors.
- Wiring or Connector Issues – Corrosion, damage, or loose connections can cause signal interruptions.
- ECM Malfunction – Rare, but a failing ECM could misinterpret signals.
- Vacuum Leaks – Can lead to erratic throttle readings.
How to Fix P0121 in a Toyota
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Check and Clean the Throttle Body
- Use throttle body cleaner to remove carbon buildup.
- Inspect for any obstructions in the throttle plate movement.
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Inspect and Test the TPS Sensor
- Use a multimeter to check voltage (should vary smoothly as throttle opens and closes).
- Replace the TPS sensor if readings are inconsistent.
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Check Wiring and Connectors
- Look for damaged, loose, or corroded wires around the throttle body and ECM.
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Reset the ECM
- Disconnect the battery for about 10 minutes to reset the system after making repairs.
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Perform a Throttle Relearn Procedure
- Some Toyota models require a throttle position relearn after replacing or cleaning components.
If the Code Persists
- Consider checking the accelerator pedal position sensor (APP).
- If no faults are found in the throttle system, the ECM may need reprogramming or replacement.
Would you like a specific guide for your Toyota model? Let me know! 🚗💨