Code
P2127
HUMMER
P — Powertrain
Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in APP sensor 2 circuit (open to ground or short to ground)
- Corroded, loose, bent or damaged connector/terminal at pedal or PCM
- Failed APP sensor (sensor 2 internal short or internal fault)
- Loss of 5V reference or poor ground to the sensor
- PCM input circuit fault
- Contamination or mechanical damage to pedal assembly
Symptoms
- Check Engine MIL / DTC P2127 stored
- Reduced engine power / limp-home mode
- Poor or unresponsive throttle / hesitations
- Possible engine starts and runs but throttle response limited
- Possible intermittent faults if wiring is damaged
What to check
- Read freeze frame and live PID data for APP sensor 1 and sensor 2 with a scan tool
- Visually inspect pedal assembly connector and wiring harness for damage, corrosion, or pin push-out
- Back-probe connector and measure sensor 2 signal voltage with key ON engine OFF
- Compare APP sensor 1 and sensor 2 voltages while moving the pedal slowly
- Check for proper 5V reference and ground at the pedal connector
- Wiggle harness and connectors while watching live data for intermittent changes
Signal parameters
- 5V reference supply present at sensor (approx. 5.0 V key ON)
- Sensor 2 signal expected to vary across pedal travel within approx. 0.2–4.8 V (model dependent)
- Low-voltage fault typically detected when sensor 2 signal is below ~0.2–0.5 V or out of expected range
- Sensor 1 vs Sensor 2 should show correlated but not identical curves; gross mismatch indicates wiring/sensor fault
Diagnostic algorithm
- Connect a scan tool, record freeze frame and live PIDs for APP sensor 1 and sensor 2. Note voltages at rest and during pedal travel.
- Visually inspect pedal connector, wiring, and PCM connector for damage, corrosion, bent pins, or water intrusion. Repair any obvious damage.
- With key ON engine OFF, back-probe the pedal connector: verify 5V reference, sensor 2 signal voltage, and ground presence. If 5V or ground missing, trace back to PCM/ground point.
- Slowly depress and release the pedal while watching sensor 2 signal. If the signal remains at or near 0 V (low) while sensor 1 changes, suspect sensor 2 circuit problem or sensor failure.
- Check continuity/resistance between sensor 2 signal pin and PCM input pin with harness unplugged (power off). Look for opens or short to ground/battery.
- If wiring and connectors are good and 5V/ground present, replace the pedal assembly or APP sensor per manufacturer procedure and re-test.
- If replacement sensor still shows low, check PCM input circuit and reference supply; consult wiring diagrams and perform PCM bench or module diagnostics as required.
- Clear codes and perform a road test to verify the fault does not return. Document intermittent conditions if present.
Likely causes
- Damaged/loose connector or terminal at the pedal harness
- Broken/shorted wiring between pedal sensor 2 and PCM (open to ground or short to ground)
- Failed APP assembly (sensor 2 internal failure)
- Loss of 5V reference or poor ground at sensor
Fault status
Status
Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage — voltage below expected range on APP sensor 2 circuit. PCM may enable limp mode.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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