Code
P2122
HUMMER
P — Powertrain
Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage
AI status
Completed
Completed
100%
Causes
- Damaged or shorted APP sensor 1 signal wire (short to ground)
- Loose, corroded, or disconnected connector/pins at the pedal sensor
- Failed or internally shorted accelerator pedal position sensor (APP sensor 1)
- Poor ground or low reference supply (5V) from ECU/PCM
- Intermittent wiring damage from routing or harness chafing
- Faulty PCM (rare)
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated (check engine light)
- Reduced engine power / limp-home mode or limited throttle response
- Hesitation or poor throttle response
- Possible stored or simultaneous throttle/pedal correlation codes
- Vehicle may start normally but throttle is unresponsive or limited
What to check
- Read freeze frame data and related codes with a scan tool; note when code set (engine temp, vehicle speed, pedal position)
- View live data for APP sensor 1 voltage and APP sensor 2 (if present) while key ON engine OFF and during pedal travel
- Perform visual inspection of pedal connector and harness for damage, corrosion, pin push-out, or moisture
- Check battery voltage and chassis/engine grounds before testing sensors (stable >12V)
- Wiggle harness and connector while monitoring live data to look for intermittent changes
Signal parameters
- Reference supply: approx. 5.0 V (typically ~4.8–5.2 V) from PCM to sensor
- Signal voltage at key ON, pedal at rest: approx. 0.4–0.8 V (low end)
- Signal voltage at mid pedal travel: ≈2.0–2.8 V
- Signal voltage at wide-open pedal: approx. 3.8–4.8 V
- Low-voltage fault threshold: signal significantly below expected rest value (often
- Sensor ground: near 0 V (check for low resistance to chassis ground)
Diagnostic algorithm
- Connect a scan tool and confirm P2122 plus any related codes (APP sensor 2, throttle body codes). Record live APP voltages and behavior with key ON engine OFF and with pedal travel. Note whether code is current or historic.
- Visually inspect pedal assembly connector and harness. Repair visible damage, bent pins, corrosion, or contamination before further testing.
- With key ON engine OFF, backprobe the APP sensor connector: verify reference 5V supply from PCM, sensor ground, and APP1 signal voltage. Compare to expected signal_params. If reference or ground missing/low, trace back to PCM, fuses, and grounds.
- If reference and ground are good but APP1 signal is low, check for short to ground on the signal wire: disconnect the pedal sensor and measure signal circuit voltage at the harness side. If disconnected harness still reads low (near ground), there is a short in wiring. If it reads correct voltage (open/float), the sensor is likely shorted internally.
- Perform continuity/resistance checks: measure resistance between signal wire and chassis ground for a short; inspect resistance/continuity of reference and ground circuits to PCM per service manual. Wiggle harness while observing readings for intermittent faults.
- If wiring and connectors check OK, test or replace the APP sensor per service manual procedure (bench or on-vehicle) and re-check live data for plausible voltage sweep with pedal travel. Compare sensor 1 vs sensor 2 (if present) for correlation.
- Repair any damaged wiring or connector faults. After repairs or sensor replacement, clear codes, perform relearn procedures if required by manufacturer, then road test and confirm the fault does not return.
- If wiring, connector, and replacement sensor fail to resolve the low voltage, suspect PCM output or internal fault and consult manufacturer guidance; consider professional PCM testing/repair.
Likely causes
- Shorted signal wire to ground between pedal and PCM
- Corroded/poor connector at the APP sensor
- Failed APP sensor 1
- Open or weak reference 5V or ground at the sensor
- Intermittent wiring damage due to movement at pedal mounting
Fault status
Status
APP Sensor 1 signal voltage is lower than expected. ECM detected low-voltage condition on accelerator pedal sensor 1 circuit.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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