Code
P1275
HUMMER
P — Powertrain
Accelerator Pedal Position (APP) Sensor 1 Circuit
AI status
Completed
Completed
100%
Causes
- Damaged, broken or chafed wiring in APP Sensor 1 circuit
- Corroded or loose connector pins at pedal sensor or ECM
- Open or short to ground/5V in signal or reference wiring
- Failed APP Sensor (internal electrical fault)
- Contaminated or water-damaged pedal sensor
- Faulty PCM/ECM (rare)
Symptoms
- MIL/Check Engine light illuminated
- Reduced engine power / limp mode
- Poor or delayed throttle response
- Vehicle may stall or hesitate under acceleration
- Unusual throttle surging or inconsistent idle
- Stored faults for related pedal/throttle position circuits
What to check
- Read DTCs and freeze frame data with a scan tool; note related codes (P0120–P0223, P2138/P2135).
- Confirm battery voltage is within specification (12.4–14.5 V) before testing.
- Visually inspect APP sensor connector and wiring harness for damage, corrosion, or water intrusion.
- Backprobe sensor connector and verify 5V reference and good ground at idle and while moving pedal.
- Measure APP Sensor 1 signal voltage at rest and through full pedal travel; look for smooth change without dropouts.
- Perform wiggle test on wiring while monitoring live data to look for intermittent faults.
Signal parameters
- Reference (Vref): typically 5.0 V (check factory spec)
- Sensor 1 signal voltage at rest (pedal released): ~0.5–1.5 V (vehicle dependent)
- Sensor 1 signal voltage at full pedal: ~3.5–4.5 V (vehicle dependent)
- Sensor output should move smoothly and monotonically with pedal position (no sudden jumps/dropouts)
- Redundant sensor channels or a second pedal sensor (if present) should correlate; large disagreement flags a fault
Diagnostic algorithm
- Retrieve all stored codes and freeze frame data. Note any additional throttle or sensor codes.
- Inspect pedal area and wiring harness for physical damage, rodent chew, water, or corrosion. Repair any visible damage.
- Verify battery and chassis/engine grounds are secure and within specification.
- With key on engine off, backprobe APP sensor connector: confirm Vref (~5 V) and solid ground.
- With a scan tool monitoring APP Sensor 1 voltage/percentage, slowly operate the pedal and observe signal behavior. Look for smooth change from low to high voltage. If no change or erratic, continue.
- If signal is stuck high/low or erratic, check continuity between APP sensor signal pin and PCM signal pin for open or short. Repair wiring as needed.
- Check for short to battery or ground by measuring resistance/presence of voltage on the signal wire with harness disconnected (follow manufacturer procedures).
- If wiring and connectors are good but the signal is out of specification, replace the APP sensor assembly. Use OEM part when possible.
- After repair, clear codes, perform key-on/engine-start checks, and test drive to verify the fault does not return.
- If fault persists after sensor and wiring repairs, inspect PCM connector and grounds; consider ECM diagnosis or replacement per manufacturer guidance.
Likely causes
- Open or shorted signal wire between APP sensor and PCM
- Corroded/poor connector at pedal sensor
- Failed APP sensor (internal)
- Poor ground or reference voltage supply to sensor
Fault status
Status
The engine control module has detected an abnormal signal from the Accelerator Pedal Position (APP) Sensor 1 circuit. The vehicle may enter reduced-power mode and the Check Engine Light will be on. Inspect the pedal sensor, its connector and wiring for faults before replacing parts.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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