P0122 on the 6.7L Cummins is an accelerator pedal position (APP) sensor 1 circuit low input fault. The 6.7L is drive-by-wire, so there is no throttle cable; instead the pedal contains position sensors that tell the ECM how far you are pressing. When the ECM reads the sensor 1 signal voltage below its normal range, it stores P0122 and typically drops the truck into a reduced power or idle-only state for safety.
Because the accelerator pedal is the driver's only fueling request on this engine, the ECM treats a bad pedal signal very conservatively. A single circuit fault will often leave you with a truck that starts and idles but will not rev, which understandably feels alarming. The good news is that P0122 is almost always a wiring, connector, or pedal assembly problem rather than an engine failure, so it is usually a straightforward repair once the circuit is traced.
What P0122 means
The APP sensor sends a voltage that rises as you press the pedal. The 6.7L uses two or three signals for redundancy so the ECM can catch a fault. P0122 sets when sensor 1 voltage stays too low, indicating a short to ground, an open in the signal or reference wire, or a failed pedal sensor. The ECM then limits fueling because it cannot trust the driver's request.
Common causes
- Failed accelerator pedal position sensor assembly
- Signal wire shorted to ground or chafed against the body
- Open or broken 5-volt reference or signal wire
- Corroded, loose, or backed-out pedal connector
- Water intrusion in the pedal connector or harness
Symptoms
- Reduced power, limp mode, or no throttle response
- Engine stuck at idle and will not rev
- Check engine light with P0122 stored
- Surging or erratic idle in some cases
- Companion pedal or throttle codes such as P0222 or P2138
How to diagnose it
Start with a scan tool and view the APP sensor 1 voltage and percentage while you press the pedal. A reading pinned near zero confirms the low circuit fault. Inspect the pedal connector for corrosion, water, and spread pins, since moisture in the footwell is a common culprit. With the key on, back-probe the connector and confirm the 5-volt reference is present and the ground is good. Check the signal wire for continuity back to the ECM and for a short to ground. If the reference and ground are good but the signal stays low, the pedal sensor is the likely fault.
How to fix it
Repair any shorted or open wiring and clean or replace a corroded connector first, as these are cheap fixes that resolve many P0122 cases. If the reference and ground reach the pedal but sensor 1 still reads low and does not respond, replace the accelerator pedal position sensor assembly, which is a single serviceable unit on the 6.7L. After the repair, clear the code, confirm the pedal signal sweeps smoothly from idle to full, and road test to verify normal throttle response. For the correct pedal assembly or connector pigtail for your truck, contact sales@coredieselparts.com and we will match it to your VIN.
Frequently asked questions
Can I drive with P0122 on my 6.7L Cummins?
Usually not far. The truck often will not rev past idle or is in reduced power, which is unsafe in traffic. Diagnose and repair the pedal circuit before driving.
Is P0122 the pedal or the ECM?
It is almost always the pedal sensor or its wiring. The ECM rarely fails in a way that sets this code, so check the connector and pedal assembly first.
Why does water cause P0122?
The pedal connector sits low in the cab. Water and salt corrode the pins and can short the signal to ground, dragging the voltage low and setting the code.
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