Code
P1125
SATURN
P — Powertrain
Accelerator Pedal Position APP System
AI status
Completed
Completed
100%
Causes
- Faulty accelerator pedal position (APP) sensor assembly
- Open, shorted, or corroded wiring or connectors in the APP sensor circuits
- Poor or intermittent sensor ground or 5V reference supply
- Contaminated or damaged pedal connector or harness (pin corrosion, water intrusion)
- ECM/PCM internal fault or poor connection at module
- Mechanical binding or sticking of the throttle linkage/pedal
Symptoms
- Check Engine/MIL lamp illuminated
- Reduced engine power / limp-home mode
- Throttle hesitation or unresponsive accelerator
- Cruise control disabled
- Possible stored related throttle or ECM codes
What to check
- Retrieve freeze frame and all stored/related codes with a scan tool
- Visually inspect APP sensor connector and wiring for damage, corrosion, or pin push-out
- Check battery voltage and vehicle grounding condition
- Backprobe APP sensor signal, reference (5V) and ground wires; observe voltages with pedal at rest and wide open
- Compare both APP sensor outputs (if dual-sensor design) for expected correlation and smooth change with pedal movement
- Wiggle harness and pedal while monitoring signals to reproduce intermittent faults
Signal parameters
- Reference supply: approximately +5 V (check for stable 4.75–5.25 V)
- Sensor 1 (APP A) typical idle/rest: ~0.4–1.0 V; at full travel: ~4.0–4.5 V
- Sensor 2 (APP B) often inverse or different slope: rest ~4.0–4.5 V; full travel ~0.4–1.0 V (varies by design)
- Both sensor signals should change smoothly with no sudden jumps or dropouts
- Correlation: the two sensor outputs should track and remain within manufacturer-specified tolerance and relationship
Diagnostic algorithm
- Connect a professional scan tool, read DTCs and freeze frame data. Note any other throttle/APP codes and historic intermittent flags.
- Perform visual inspection of pedal harness, connector and ECM connector for damage, corrosion or loose pins.
- With key on (engine off), backprobe the APP connector: verify stable +5V reference and a good ground. If ref or ground missing, diagnose supply/ground circuit before replacing sensor.
- Start vehicle or use scan tool to view live data: slowly press and release the accelerator while observing both APP sensor voltages. Look for smooth travel, correct voltage ranges and proper correlation between sensors.
- Wiggle the harness and move the pedal to try to reproduce the fault. If intermittent, inspect for chaffing at flex points and repair wiring or connector.
- If a sensor output is out of range or doesn't change as expected, measure continuity and for shorts to voltage/ground between the pedal connector and ECM. Repair wiring as needed.
- If wiring, connectors and supply/ground are good but sensor signals are incorrect, replace the accelerator pedal assembly (APP sensor).
- After repair, clear codes, perform any required throttle/pedal relearn or idle relearn procedure, then road test to confirm code does not return.
- If code persists after sensor/harness replacement, consider ECM/PCM diagnosis or replacement and verify ECM power and grounds.
Likely causes
- Damaged APP sensor wiring harness where it flexes with pedal movement
- Loose or corroded connector at the pedal sensor
- One sensor output is out of expected voltage range while the other is normal
- Short to voltage or short to ground on one of the sensor signal wires
- Failed APP sensor inside the pedal assembly
Fault status
Status
The ECM has detected an abnormal signal or correlation from the Accelerator Pedal Position (APP) sensor circuit. When P1125 is set the controller may limit engine power and disable cruise control to protect drivability and safety.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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