P0123 - Throttle/Pedal Position Sensor/Switch A Circuit High Input
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0123 is set when the Engine Control Module (ECM) detects that the Throttle Position Sensor (TPS) or Pedal Position Sensor (APP) 'A' circuit voltage is higher than the calibrated limit (typically above 4.5V to 4.8V). The sensor uses a 5V reference and returns a signal based on throttle angle. A 'High Input' condition usually indicates a short to voltage in the signal wire, a loss of ground (open ground circuit), or an internal sensor failure. High-side failures trigger safety protocols, often limiting engine RPM or throttle response (Limp Home Mode).
Possible Causes
Faulty Throttle Position Sensor (TPS) / APP sensor
Open circuit in the sensor ground wire (causes signal to float high)
Short to voltage (12V or 5V ref) on the signal wire
Corroded or damaged connector pins
Internal Engine Control Module (ECM) fault
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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