Code
P2120
HUMMER
P — Powertrain
Accelerator Pedal Position (APP) Sensor 1 Circuit
Views:
UK: 21
EN: 65
RU: 44
AI status
Completed
Completed
100%
Causes
- Damaged or shorted APP sensor wiring harness (open, short to ground or to 5V reference)
- Poor or corroded connector pins at the APP sensor or ECM
- Failed/contaminated/faulty APP sensor (sensor 1)
- Poor ECM power or ground connection
- Water intrusion or physical damage at connector or sensor
- Intermittent connection due to broken wire or terminal
Symptoms
- Malfunction Indicator Lamp (MIL) on (CEL)
- Reduced engine power / limp-home mode / limited throttle response
- Delayed, erratic, or no throttle response to pedal input
- Poor idle or hesitation on acceleration
- Possible stored or multiple throttle/pedal-related DTCs (e.g., correlation faults)
What to check
- Retrieve DTC(s) and freeze-frame data with a scan tool
- Inspect APP sensor connector and harness for damage, corrosion, pin push-out, or water entry
- Visually check ECM connectors and engine grounds related to throttle/pedal circuits
- Verify battery voltage and fuse(s) for ECM/throttle control system
- Use a scan tool to view live APP sensor 1 (and sensor 2) voltage/position data while operating the pedal
- Perform a wiggle test of the harness and connector while observing live data for intermittent faults
Signal parameters
- Reference (VREF) to sensor: ~5.0 V (typically 4.75–5.25 V) while ignition on
- Sensor 1 output: typically ≈0.5–4.5 V across pedal travel (idle/closed ~0.5–1.0 V; wide open >4.0 V)
- Sensor 2 (redundant) typically provides a second signal that should correlate but not be identical (often offset or inverse)
- No short to ground (0 V) or to VREF (≈5 V stuck) expected on signal line
- Smooth, monotonic change in voltage with pedal travel (no dropouts or jumps)
Diagnostic algorithm
- Connect a scan tool, record PIDs and any additional codes. Note freeze-frame data and key on engine off (KOEO) voltages.
- Visually inspect APP sensor connector, wiring harness, and nearby components for physical damage, corrosion, or water contamination. Repair obvious damage.
- With key ON (engine off), backprobe the APP connector: verify VREF (~5 V), sensor 1 signal voltage, and sensor ground. Compare to expected signal_params. If VREF absent, trace power/fuse/ECM supply.
- Operate the accelerator pedal while watching live PID for sensor 1. Confirm smooth change from low to high voltage. If signal is stuck, erratic, or out-of-range, suspect sensor or wiring.
- Check continuity between the APP sensor signal and the ECM pin (ignition off). Look for opens or high resistance. Inspect for unintended continuity to ground or battery positive (shorts).
- Perform a wiggle/movement test on harness and connector while monitoring live data to find intermittent faults.
- If wiring and connector check good and signal still abnormal, replace the APP sensor. Reconnect and re-test live data.
- Clear codes and road test to confirm repair. If fault returns and wiring/sensor are verified good, consider ECM or module-side fault and further bench or module diagnostics.
Likely causes
- Faulty APP sensor 1
- Broken or chafed signal wire between APP sensor and ECM
- Corroded/loose connector at pedal assembly
- Short to battery voltage or ground in the APP harness
Fault status
Status
P2120 — APP Sensor 1 Circuit: The ECM detected an abnormal or out-of-range signal from the accelerator pedal position sensor 1 circuit. This may be caused by an open or shorted signal, bad sensor, poor connector, or ECM/power/ground issue and often results in reduced power/limp mode.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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