Throttle/Pedal Position Sensor A Circuit High
The Powertrain Control Module (PCM) detected that the voltage signal from Throttle/Pedal Position Sensor A is higher than the expected normal operating range. This typically means the sensor's output voltage exceeded the maximum threshold (usually around 4.5 to 4.9 volts) for a specified amount of time.
This code is considered high severity because a faulty throttle position sensor can cause unpredictable engine behavior, stalling, or force the vehicle into a restricted limp mode. It should be diagnosed and repaired immediately to ensure safe vehicle operation.
Common symptoms
- Check Engine Light is illuminated
- Engine hesitates or stumbles during acceleration
- Vehicle enters a restricted power limp mode
- High or erratic engine idle speed
- Engine stalls unexpectedly while driving or coming to a stop
Likely causes
- Defective Throttle Position Sensor (TPS) or Pedal Position Sensor (PPS)
- Short to power in the TPS/PPS signal wire
- Broken or disconnected sensor ground wire
- Corroded, damaged, or loose electrical connector at the sensor
- Improperly installed or misadjusted Throttle Position Sensor
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Visually inspect the TPS/PPS wiring harness and connector.
Look for: Look for frayed wires, melted insulation, or a loose/corroded connector that could cause a short to voltage or an open ground circuit.
Monitor live TPS voltage using an OBD-II scan tool.
Look for: With the key on and engine off, the TPS voltage should smoothly increase from about 0.5V to 4.5V as you press the pedal. A constant reading near 5V indicates a hard fault.
Test the sensor ground circuit with a digital multimeter.
Look for: Check for continuity to ground at the sensor connector. High resistance or an open circuit means the sensor cannot pull the reference voltage down, causing the high signal code.
Measure the 5-volt reference and signal wires at the sensor connector.
Look for: Ensure the reference wire has exactly 5 volts. If the signal wire also shows 5 volts while disconnected from the sensor, there is a short to power in the wiring harness.
Perform a sweep test on the Throttle Position Sensor itself using a multimeter.
Look for: Measure resistance across the sensor pins while slowly opening the throttle. The resistance should change smoothly without any spikes or drop-offs; if it jumps to an open limit, the sensor is internally faulty.
This page explains the generic P0123 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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