What is the 'D' pedal position sensor?

Drive-by-wire accelerator pedals contain more than one position sensor for redundancy, and 'D' and 'E' are designations for those separate sensor channels within the pedal. They produce different but correlated signals so the PCM can cross-check them and detect a fault in either one. P2123 is specifically about the 'D' channel reading high — above its expected voltage range. Having two channels is a deliberate safety design: if one disagrees or goes out of range, the PCM knows something is wrong and reduces power rather than trusting a bad signal.

Why did my car lose power with P2123?

Because the accelerator pedal signal is safety-critical in a drive-by-wire system. When the 'D' sensor reads out of range, the PCM can no longer trust the pedal input pair, so it deliberately falls back to a reduced-power or limp mode — limiting throttle to keep the car controllable rather than risk acting on a faulty signal. The lost power is the system protecting you, not a mechanical failure of the engine. Restoring a correct pedal signal normally returns full power once the fault is fixed and cleared.

How is P2123 different from P2122?

They're mirror images on the same 'D' pedal sensor circuit. P2122 is 'circuit low input' — the signal is below the expected range, usually from a short to ground or an open. P2123 is 'circuit high input' — the signal is above the range, usually from a short to voltage or a circuit biased high. They share the same diagnostic approach and the same safety response (reduced power), but the wiring fault you're hunting is opposite: low points toward ground shorts, high points toward voltage shorts.

Is it safe to drive with P2123?

It's usually driveable enough to get off the road or to a shop, but you shouldn't plan to keep driving it. In limp mode the throttle is limited, so acceleration is sluggish — which can itself be a hazard when merging or crossing traffic. There's no mechanical engine damage risk from the fault, but the reduced and potentially unpredictable throttle response is a safety concern. Get it diagnosed promptly, and drive cautiously and minimally until the pedal signal is restored to normal.

OBD-II trouble code

P2123: Throttle/Pedal Position Sensor 'D' Circuit High Input

The 'D' accelerator pedal position sensor is reading too high — a signal voltage above its expected window. As the high-input mirror of P2122, it usually traces to a short to voltage, a connector or wiring fault, or a failed pedal sensor. Because drive-by-wire systems treat pedal signals as safety-critical, this often comes with reduced-power limp mode until it's resolved.

Quick facts

System: Powertrain
Category: Throttle / Idle
Severity: High severity
Drivable: Usually safe to drive short-term
Repair cost range: $150 – $450
DIY difficulty: Intermediate DIY

What does P2123 mean?

In a drive-by-wire (electronic throttle) system there's no cable between the accelerator pedal and the throttle. Instead, the pedal contains redundant position sensors that tell the PCM how far the driver is pressing, and the PCM opens the electronic throttle accordingly. The redundancy is a safety feature: the sensors output different but correlated signals so the PCM can cross-check them and catch a fault. 'D' refers to one of those pedal position sensor channels. P2123 sets when the D sensor's signal voltage stays above the expected range — the circuit-high condition, the mirror of P2122 (circuit low). Since the pedal signal directly controls engine power, the PCM treats an out-of-range reading as serious.

The causes are electrical. A short to a voltage source in the D signal wire is the classic high-input cause, often where a harness chafes against a powered circuit. A corroded or damaged connector that biases the reading up, a failed pedal position sensor outputting high, a wiring fault, or a problem with the sensor's reference or ground can all push the signal above spec. Because the pedal assembly houses the sensors, a failed sensor usually means replacing the pedal module on most vehicles. The PCM continually compares the D and E pedal signals; when one goes out of range, it can no longer trust the pair, so it falls back to a safe, reduced-power strategy.

For the driver, P2123 commonly brings a check engine light and a noticeable loss of power — the throttle may be limited, acceleration sluggish, and the car may enter a limp/failsafe mode that caps speed to keep things safe. Idle may be affected and, in some cases, the engine may be hard to rev. The car is usually driveable enough to get off the road or to a shop, but the reduced power is deliberate. Diagnosis reads both pedal sensor signals, checks the D circuit for a short to voltage, inspects the connector and reference/ground, and replaces the pedal sensor assembly if the circuit is good but the sensor reads high.

Common causes

Short to a voltage source in the 'D' pedal sensor signal wire
Corroded or damaged pedal sensor connector biasing the reading high
Failed accelerator pedal position sensor outputting high
Wiring fault feeding voltage into the signal circuit
Problem with the sensor's reference voltage or ground
Chafed harness contacting a powered circuit
Damage after pedal or harness service

Symptoms

Check engine light with P2123 stored
Reduced engine power or limp / failsafe mode
Sluggish or limited acceleration
Throttle that feels unresponsive
Idle or revving irregularities
Possible companion pedal-position codes

Diagnostic steps

1.Read both pedal position sensor signals in live data and confirm the 'D' channel reads high or out of range.
2.Check the 'D' signal wire for a short to voltage, inspecting where the harness could chafe against a powered circuit.
3.Inspect the pedal sensor connector for corrosion, damage, and looseness.
4.Verify the sensor's reference voltage and ground are within spec.
5.Test wiring continuity back to the PCM for faults that would skew the reading.
6.Replace the pedal position sensor assembly if the circuit, reference, and ground are good but the sensor still reads high.

Repair cost

$150 – $450

An accelerator pedal position sensor is usually integrated into the pedal assembly, so replacement runs roughly $150-$400 with labor depending on the vehicle. A wiring or connector repair can be less but takes diagnostic time to locate a short to voltage. Because the system is safety-critical, confirm the circuit and both sensor signals before replacing the pedal module.

Estimate your repair

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Open the Repair Cost Estimator with accelerator pedal position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.

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DIY vs shop

This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.