P0123 Code: Throttle/Pedal Position Sensor/Switch A Circuit High Input
Quick Answer
The throttle position sensor is sending a higher voltage than the ECU expects, suggesting a wide-open throttle signal even when the pedal isn't pressed.
At a Glance
What this code means
P0123 means the TPS output voltage is above the maximum acceptable threshold. The ECU sees a signal indicating full throttle even when the pedal is at rest. This is the opposite condition from P0122 and typically points to a short to voltage in the signal wire, a failed sensor, or a miscalibrated sensor.
Common causes
- Faulty TPS with failed internal resistance track
- Short to voltage in the TPS signal wire
- Damaged or shorted TPS connector
- Out-of-adjustment TPS (on older mechanical systems with adjustable sensors)
- Throttle body failure on integrated electronic throttle systems
Symptoms you might notice
- Vehicle may surge or accelerate unexpectedly (dangerous)
- Rough idle or high idle
- Engine may enter limp mode as a safety measure
- Hesitation and erratic throttle response
- Check engine light on
Can you still drive?
No — not safely. A high-voltage TPS signal can cause unintended acceleration. Have the vehicle inspected before driving.
How serious is this code?
High. Unintended acceleration or limp mode makes this a safety concern. Address immediately.
Before you replace parts
Parts replacement is often not the first step. Before buying anything, it's worth checking these basics:
- Check TPS voltage with ignition on, engine off — it should read approximately 0.5V at idle, not close to 5V
- Wiggle the wiring harness near the connector while watching live TPS data — an intermittent short in the harness will show up as voltage spikes
How to troubleshoot it
- Check the TPS wiring connector for a short to voltage or damaged insulation
- Use a multimeter to measure TPS signal voltage at rest — should be approximately 0.5V (not near 4.5–5V)
- On adjustable TPS systems, check and reset the sensor adjustment
- Test the reference voltage at the TPS connector — should be 5V from the ECU
- Replace the TPS if voltage at rest is near the maximum
Tools that may help
These are the types of tools commonly used when diagnosing this code. Having the right tool can save time and help confirm a diagnosis before spending money on parts.
- Multimeter
- OBD-II scanner with live TPS voltage data
Estimated repair cost range
TPS replacement: $50–$200. Electronic throttle body with integrated TPS: $150–$400.
Costs vary significantly by vehicle, location, and whether you use OEM or aftermarket parts. These are general ranges for reference only.
When to call a mechanic
If you've completed the basic troubleshooting steps and the code keeps returning, or if you don't have access to the proper diagnostic tools, it's worth consulting a professional. A qualified technician can perform a full diagnosis and confirm the root cause before any parts are purchased. When in doubt, get a professional opinion — it can save you from an expensive misdiagnosis.
Real-world note
Always verify TPS voltage at rest with the ignition on but engine off before replacing the sensor. Many TPS-related codes come from wiring harness damage rather than the sensor itself.
Informational purposes only. This guide is for educational reference and is not a substitute for diagnosis by a qualified technician. Repair costs, causes, and symptoms may vary by vehicle make, model, year, and condition. Always consult a licensed mechanic before performing major repairs.