P0123 OBD2 Code Guide
P0123 is a sensors diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Throttle/Pedal Position Sensor/Switch A Circuit High Input
Code P0123 signifies that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a voltage signal from the Throttle Position Sensor (TPS) or Accelerator Pedal Position (APP) Sensor 'A' circuit that is consistently higher than the specified maximum allowable threshold. This typically means the sensor is reporting a throttle opening that is either stuck wide open, or the circuit itself has a short to voltage, indicating an electrical issue rather than a mechanical one. This high voltage input can lead to erratic engine behavior, including high idle, lack of throttle response, or activation of limp mode.
Code verification standard
P0123 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0123 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0123 diagnostic path
- 1Begin with a thorough visual inspection of the TPS/APP sensor and its wiring harness. Look for any signs of damage, corrosion, frayed wires, or loose connections. Pay close attention to the connector pins for bending or pushed-out terminals.
- 2Connect an OBD2 scan tool and monitor the live data stream for the TPS/APP 'A' sensor voltage. With the ignition on and engine off, the voltage should typically be between 0.5V and 1.0V at closed throttle and increase smoothly to around 4.5V-5.0V at wide-open throttle (WOT). A P0123 code suggests the voltage is consistently above 4.5V-5.0V even at closed throttle. Also, check for any related codes (e.g., P0122, P0222, P0223).
- 3Disconnect the TPS/APP sensor connector. Using a multimeter, check for proper reference voltage (typically 5V) and ground at the sensor connector. Then, test the signal wire for continuity back to the ECM/PCM and for any short to voltage or ground. A high input code often points to a short to the 5V reference or a faulty sensor internally shorted.
- 4If the sensor and wiring test good, physically inspect the throttle body (for TPS) or accelerator pedal assembly (for APP) for any mechanical binding, debris, or damage that might prevent the throttle plate or pedal from returning to its fully closed position. Ensure the throttle plate moves freely and snaps back.
Verify before repair
- - Replace the Throttle Position Sensor (TPS) or Accelerator Pedal Position (APP) Sensor: This is the most common fix if the sensor itself is faulty and outputting an incorrect high voltage signal.
- - Repair/Replace Damaged Wiring or Connector: Address any identified shorts to voltage, open circuits, or corrosion in the TPS/APP sensor's wiring harness or connector.
- - Clean Throttle Body: If the throttle plate is sticking due to carbon buildup, cleaning the throttle body can resolve mechanical issues preventing the sensor from reading correctly.
- - Replace Throttle Body Assembly: In some cases, especially with electronic throttle control (ETC) systems, the TPS is integrated into the throttle body and may require replacing the entire assembly if the sensor is not separately serviceable.
Vehicle-specific pages to check next
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