OBD-II Code P2123 — What It Means & How to Fix It

What Does This Error Mean?

P2123 means the Throttle/Pedal Position Sensor D circuit voltage is too high. This is the opposite of P2122 — instead of a low voltage signal, the sensor D circuit is sending a voltage above the maximum allowed. The accelerator pedal position sensor is sending a signal that suggests the pedal is fully floored even when it is not. This is a potentially dangerous fault — the PCM may see an unintended wide-open throttle command. Limp mode is typically activated immediately when P2123 is set.

Affected Models

Common across all modern vehicles with electronic drive-by-wire throttle
Frequently seen in Ford, GM, Dodge, Toyota, and Honda models
Common in Dodge Ram and Durango
Seen in many Chevrolet and GMC truck models

Common Causes

Faulty accelerator pedal position (APP) sensor with a short-to-voltage in the signal circuit
Damaged wiring — sensor signal wire shorted to the 5-volt reference wire
Moisture or corrosion in the APP sensor connector creating a voltage bridge
APP sensor internal failure causing the signal to peg at maximum voltage
PCM input circuit fault reading voltage higher than actual

How to Fix It

Place the vehicle in Park and do not drive it until the fault is diagnosed. P2123 can indicate a false wide-open throttle signal — a safety risk.

A stuck high throttle signal is more dangerous than a stuck low signal — the vehicle could unexpectedly accelerate.
Inspect the APP sensor connector for moisture, corrosion, or pins that may be bridging between circuits.

Even a small amount of water in the connector can cause the signal wire to short to the reference voltage wire.
Disconnect the APP sensor connector and check if the P2123 code clears or changes to P2122 (low voltage).

If the code changes to low voltage with the sensor disconnected, the wiring harness is likely shorted to voltage — not the sensor itself.
Measure the APP sensor signal voltage at the connector with the key on (engine off). It should be near 0.5 volts at rest with the pedal up.

A voltage reading above 4.0 volts at rest confirms either a sensor failure or a wiring short to voltage.
Replace the accelerator pedal assembly if the sensor is at fault, or repair the wiring if a short is found.

Inspect the full wiring harness from the pedal to the PCM before replacing the pedal assembly.

When to Call a Professional

Accelerator pedal assembly replacement is $50 to $200 in parts. Labor is typically 30 to 60 minutes. Total shop cost is $100 to $350. Professional diagnosis is recommended since high-voltage faults can indicate wiring shorts requiring careful inspection.

Frequently Asked Questions

Is P2123 more dangerous than P2122?

Generally, yes. P2122 (low voltage) typically results in a no-power or very limited power condition — the car barely moves. P2123 (high voltage) can make the PCM think you are flooring the throttle when you are not. The PCM's safety systems should prevent actual unintended acceleration, but this code still demands immediate attention.

Can water cause P2123?

Yes — this is more common than people expect. Floor mats that have gotten wet, or water intrusion from a leaking windshield or door seal, can cause moisture to reach the APP connector under the dash. Drying out the connector and applying dielectric grease can resolve moisture-related P2123 cases.

Will P2123 cause my car to stall?

Not directly — a high pedal signal usually triggers limp mode rather than a stall. However, if the PCM enters a fail-safe mode that cuts fuel as a runaway throttle protection, the engine may stall. Behavior varies by make and model.