P0123 on the 6.7L Power Stroke is an accelerator pedal position (APP) sensor 1 circuit high input fault. Like all modern diesels, the 6.7L uses an electronic drive-by-wire pedal instead of a throttle cable. The pedal houses redundant position sensors, and P0123 sets when the PCM reads sensor 1 voltage above its expected range, which it interprets as an unreliable signal and responds to by limiting power.
The PCM will not simply trust a pedal signal that has gone out of range, because doing so could command unwanted fueling. Instead it defaults to a safe reduced-power mode until the fault clears. That protective behavior is why a small wiring or connector issue can feel like a serious engine problem, even though the underlying fix is typically minor once you trace the high-reading circuit.
What P0123 means
The APP sensor outputs a voltage that increases as the pedal is pressed. P0123 flags sensor 1 reading too high, which usually means the signal wire is shorted to a voltage source or to the 5-volt reference, the ground has been lost so the signal floats high, or the pedal sensor has failed. The PCM cross-checks the redundant sensors and derates when the readings disagree.
Common causes
- Failed accelerator pedal position sensor assembly
- Signal wire shorted to reference or battery voltage
- Open or high-resistance sensor ground causing the signal to float
- Corroded or loose pedal connector
- Chafed harness bridging signal and reference wires
Symptoms
- Reduced power or limp mode
- Poor or no throttle response, engine stuck near idle
- Check engine light with P0123 stored
- Erratic acceleration in intermittent cases
- Related pedal codes such as P0223 or P2138
How to diagnose it
Use a scan tool to watch APP sensor 1 voltage as you move the pedal. A value pinned high, near the reference voltage, confirms the fault. Inspect the pedal connector for corrosion, damaged pins, and a secure lock. Back-probe the connector and confirm a clean sensor ground; a lost ground is a frequent cause of a high reading. Check the signal wire for a short to the 5-volt reference or to power, and confirm continuity back to the PCM. If the ground and reference are correct but the signal stays high, the pedal sensor has failed.
How to fix it
Restore a poor ground and repair any wiring shorted to voltage, then clean or replace a corroded connector. These repairs fix the majority of P0123 faults. If the wiring checks good but sensor 1 still reads high, replace the accelerator pedal position sensor assembly. After the repair, clear the code, verify the pedal voltage sweeps correctly from idle to full throttle, and road test to confirm power returns. For the correct pedal assembly or connector for your 6.7L Power Stroke, contact sales@coredieselparts.com.
Frequently asked questions
What is the difference between P0122 and P0123?
P0122 is the pedal sensor 1 circuit reading too low and P0123 is the same circuit reading too high. Both point at the APP sensor 1 wiring or the pedal, from opposite electrical directions.
Will P0123 put my truck in limp mode?
Usually yes. The PCM cannot trust the pedal request, so it limits power to a safe level until the circuit is repaired and the signals agree again.
Can a bad ground cause P0123?
Yes. If the sensor ground is open or high in resistance, the signal floats upward and reads high. Always confirm a clean ground before replacing the pedal.
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