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DTC codes / GM codes / P1125

P1125 · GMAccelerator Pedal Position Sensor Fault

P1125 on a GM vehicle means the powertrain control module (PCM) has detected a fault in the accelerator pedal position (APP) sensor circuit, which translates the driver's foot movement into an electrical signal for throttle control. The computer compares the APP sensor signals against each other and against expected values, and it sets this code when the readings fall outside the programmed limits or become inconsistent.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • The warning light illuminates, and the vehicle may enter reduced power mode with limited engine speed
  • The accelerator pedal feels unresponsive or the engine hesitates when you press the pedal
  • The engine may idle erratically or stall when coming to a stop
  • Cruise control may stop working or refuse to engage
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty accelerator pedal position sensor assembly, worn tracks or internal electrical failure
  2. Corroded, loose, or damaged wiring or connector pins at the APP sensor or PCM
  3. Water intrusion into the pedal sensor connector or harness, common on older GM trucks and SUVs
  4. Poor ground connection for the APP sensor circuit, causing voltage reference instability
  5. Failed or misadjusted brake pedal position switch interfering with the APP signal correlation
  6. PCM software calibration issue or internal PCM fault, less common but possible

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to see the conditions when P1125 set
  2. Inspect the APP sensor connector and harness for corrosion, water intrusion, chafing, or loose pins, and repair as needed
  3. Back-probe the APP sensor signal wires and verify smooth voltage changes through the full pedal travel using a scan tool or multimeter
  4. Check the sensor reference voltage and ground circuits for drops or opens, and clean or repair grounds
  5. Test the brake pedal position switch operation and adjustment, since a faulty switch can skew APP correlation
  6. Replace the accelerator pedal assembly if sensor output is erratic or out of specification, then clear codes and perform a relearn if required
  7. If all inputs are correct, check for PCM calibration updates or diagnose the PCM as a last step

What most technicians miss on P1125

  • A weak or intermittent ground at the APP sensor can mimic a failed pedal assembly, so always load-test the ground circuit before condemning the sensor.
  • Water intrusion into the connector is a frequent cause on GM trucks and SUVs, and the corrosion often hides inside the connector body where a quick visual check misses it.
  • The brake pedal position switch shares correlation logic with the APP sensor, and a misadjusted switch can set P1125 without any pedal fault at all.
  • Intermittent P1125 codes that do not reappear during a road test often stem from harness chafing near the pedal bracket, so wiggle-test the harness while watching live data.
  • Replacing the pedal assembly without checking for a PCM calibration update can result in a repeat code if the original issue was software-related.

Can I keep driving with P1125?

You can usually drive the vehicle to a repair shop, but expect reduced engine power and avoid highways or heavy traffic because the throttle response may be unpredictable. If the vehicle enters limp mode or the pedal becomes unresponsive, stop driving and arrange a tow.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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