P0123
Throttle/Pedal Position Sensor/Switch A Circuit High Input
If your vehicle's onboard computer has flagged the diagnostic trouble code P0123, it refers to a detected anomaly regarding "Throttle/Pedal Position Sensor/Switch A Circuit High Input". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Storing code P0123 is your car's way of telling you something is wrong with the throttle/pedal position sensor/switch a circuit high input. Drivers typically experience high idle speed, erratic throttle response, check engine light when this code is active. This is a moderate-severity fault — plan a repair shop visit within the week to keep it from escalating.
Symptoms
High idle speed, erratic throttle response, check engine light
Common Causes
- Short to voltage in TPS wiring
- Faulty Throttle Position Sensor
- Loose sensor mounting screws
- Failed PCM
How to Fix
- 1 Test TPS circuit for shorts
- 2 Replace TPS sensor
- 3 Tighten and calibrate sensor position
- 4 Test PCM reference voltage
Technical Explanation
Detection of P0123 occurs when the ECM cross-references multiple sensor inputs and determines that the reported values are physically inconsistent or out-of-range. Sensor output is cross-validated against complementary sensor data (such as MAF vs. MAP correlation, or upstream vs. downstream O2 comparison) to confirm the fault is genuine and not a result of a sensor reading an actual engine condition. The MIL illuminates after the fault is confirmed on two consecutive drive cycles, and the freeze frame data captured at first detection is stored in the PCM's memory for diagnostic reference.
Is It Safe to Drive?
Medium-severity fault: the car functions but not optimally. The short to voltage in tps wiring issue will not resolve itself and will cause measurable long-term wear. A repair in the $80–$250 range now avoids far higher costs later.
Mechanic's Pro Tip
Before replacing any component on P0123, spend 5 minutes inspecting the wiring harness and connector first — corrosion, chafed insulation, and backed-out pins cause the majority of these faults and cost nothing to fix. Use a multimeter to measure voltage drop across the connector pins under load; anything above 0.1V indicates excessive resistance that will cause intermittent failures even after replacing the sensor.
TPS replacement: $80 - $200