What is the P0123 fault code?
The P0123 fault code is a generic powertrain (OBD-II) code that indicates a problem with the Throttle Position Sensor (TPS) circuit. It signals that the Powertrain Control Module (PCM) has detected an abnormally high voltage from the sensor, exceeding the manufacturer’s specified limits.
Operation of the Throttle Position Sensor (TPS)
The TPS is a potentiometer mounted on the throttle body. Its role is to measure the opening angle of the throttle valve and send a proportional electrical signal to the PCM, the vehicle’s main computer. It typically consists of three wires:
- A 5-volt reference supply from the PCM.
- A ground (earth return).
- A signal wire that returns the variable voltage to the PCM.
When the throttle is at idle (closed), the signal voltage is typically around 0.45 to 0.55 volts. At wide open throttle (WOT), this voltage should approach 5 volts. Code P0123 is triggered when the PCM detects a voltage consistently higher than the expected normal range.
Symptoms of Code P0123
A P0123 fault can manifest through several noticeable symptoms:
- Irregular or unstable idle
- Abnormally high idle speed
- Hesitation or power fluctuations during acceleration (surging)
- Stalling or difficulty starting
- Entry into limp mode
- Increased fuel consumption
Possible Causes of the P0123 Fault
Several issues can cause a P0123 code:
- Wiring problem: Short circuit to the battery in the TPS signal circuit, damaged, chafed, or corroded wires.
- Faulty TPS sensor: The internal potentiometer is worn or defective.
- Poor mounting: The sensor is loose or improperly installed on the throttle body.
- Faulty PCM: In rare cases, the computer itself may be the cause.
How to Diagnose and Resolve a P0123 Code?
1. Preliminary Check
Start by consulting your manufacturer’s Technical Service Bulletins (TSBs). It might be a known issue with a specific correction procedure.
2. Visual Inspection
Carefully inspect the TPS connector and wiring. Look for any signs of damage, corrosion, burning, or looseness. Ensure the sensor is securely fastened.
3. Electrical Measurements
Using a multimeter, measure the voltage on the TPS signal wire (engine off, ignition on).
- A voltage consistently above ~4.65 volts confirms the problem.
- Refer to your vehicle’s repair manual for precise expected values.
4. Corrective Actions
- If the wiring is damaged, repair or replace the affected wires.
- If electrical measurements are out of specification and the wiring is intact, replace the Throttle Position Sensor (TPS).
- After any repair, clear the fault codes with an OBD2 scanner and perform a road test to ensure the fault does not return.
Related Fault Codes
P0120, P0121, P0122, P0124
Conclusion
The P0123 code is often related to a simple electrical issue with the TPS sensor or its wiring. A thorough inspection and basic electrical tests usually allow for quick identification and resolution of the fault. For an accurate diagnosis, using an OBD2 scanner and the specific manual for your model is highly recommended.
Need help diagnosing your vehicle? Consult a certified professional or invest in a reliable diagnostic tool to precisely identify the source of the problem.