P2123
Throttle/Pedal Position Sensor/Switch D Circuit High Input
Encountering the engine check light code P2123 signifies an explicit mechanical or electrical operational breakdown categorized as "Throttle/Pedal Position Sensor/Switch D Circuit High Input". Professional scanner tools usually flag this subsystem loop early on.
Driver's Summary
P2123 is triggered when the PCM detects an abnormal condition associated with throttle/pedal position sensor/switch d circuit high input. You may notice vehicle forced into limp mode, erratic idle, all of which are direct consequences of this malfunction. This condition is classified as high severity. Prompt diagnosis is essential to prevent cascading damage to related components.
Symptoms
Vehicle forced into limp mode, erratic idle
Common Causes
- Short to voltage in APP sensor circuit
- Broken ground wire for pedal sensor
- Defective accelerator pedal
- Bad PCM
How to Fix
- 1 Trace and repair short to power
- 2 Repair broken ground connection
- 3 Replace accelerator pedal
- 4 Replace PCM
Technical Explanation
To set P2123, the PCM samples the affected circuit multiple times per second, comparing live readings against manufacturer-programmed operating windows. A two-trip detection strategy is employed for most powertrain codes: the fault must be detected on one drive cycle, the vehicle key-cycled off, and the fault detected again on the next drive cycle before the MIL illuminates and a permanent DTC is stored. After two failed drive cycles, the code transitions from a pending to a confirmed DTC, and the PCM activates the MIL. Clearing the code without repairing the fault will result in re-illumination within one to two complete drive cycles.
Is It Safe to Drive?
An active P2123 code under high-severity conditions means the affected system is operating outside safe parameters. Continued driving — especially under load or at highway speeds — significantly increases the risk of secondary damage to components like broken ground wire for pedal sensor.
Mechanic's Pro Tip
Module replacement should always be the last resort for P2123 after exhaustively verifying all power supply circuits, ground connections, and communication bus wiring. Use a wiring diagram to locate all fuses, relays, and ground points for the affected module, and measure voltage drop on each ground with the circuit loaded. A module "failure" is frequently a corroded ground eyelet or a weak battery causing brownout conditions — fix these first and you'll save hundreds of dollars on an unnecessary module replacement.
Pedal replacement: $150 - $350