What it means
Throttle/Pedal Position Sensor "D" Circuit High: the signal voltage is above the expected range. Often an open circuit or a short to supply voltage.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The throttle or pedal position sensor D circuit sends a position signal to the control module for comparison with other channels. P2123 sets when that signal rises above its expected range, which can happen if the signal wire is open or shorted to supply voltage, or if the sensor ground is lost.
Common causes
Most likely first.
- Signal wire shorted to supply
- Sensor ground open
- Connector pins corroded - high contact resistance
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Save freeze-frame data and compare live D-channel readings with the other pedal or throttle channels to verify that D is high and identify when it occurs.
- Inspect the D circuit connector and harness for an open signal wire, damaged insulation touching a supply wire, corrosion, or loose pins.
- Check for a short to supply voltage and verify sensor ground continuity against the wiring information and manufacturer's specification.
- Check the D signal through the connector and harness while gently moving the wiring to expose an intermittent open or poor terminal contact.
- If the circuit supply, ground, and wiring are sound, test the sensor assembly's D track using the vehicle-specific procedure.
Common fixes
- Repair an open D signal wire or insulation shorted to a supply circuit.
- Restore the sensor ground and clean or secure its connector terminals.
- Repair damaged harness sections and ensure the wiring cannot rub against adjacent components.
- Replace the position sensor assembly if the D signal remains high with a verified sound circuit.
Can I keep driving?
A high D-channel signal can trigger reduced throttle response or limp mode. Avoid driving in traffic that requires quick acceleration, and stop safely if throttle behavior becomes erratic or the vehicle no longer responds predictably.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.