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Home / DTC / P1271 — Accelerator Pedal Position (APP) Sensor 1-2 Correlation

P1271 — Accelerator Pedal Position (APP) Sensor 1-2 Correlation

Detailed page for trouble code P1271.

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P1271

HUMMER P — Powertrain

Accelerator Pedal Position (APP) Sensor 1-2 Correlation

Brand: HUMMER
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Faulty accelerator pedal position sensor (one or both sensors)
  • Damaged/shorted/open wiring or pins between APP and PCM
  • Poor connector contact, corrosion, or water ingress at pedal harness or PCM
  • Faulty PCM or internal reference/ground fault
  • Intermittent mechanical binding of the pedal or sensor
  • Aftermarket modifications, recent repairs, or software issue

Symptoms

  • Malfunction Indicator Lamp (MIL) or CHECK ENGINE on
  • Reduced engine power / limp-in mode (reduced throttle response)
  • Unresponsive or inconsistent throttle input
  • Cruise control disabled
  • Hesitation, surging, or abnormal idle when pedal moved
  • Fault may be intermittent or appear after moisture exposure

What to check

  • Read and record freeze frame data and all stored DTCs with a scan tool
  • Visually inspect pedal sensor connector, harness and PCM connector for damage or corrosion
  • Backprobe APP sensor signals and measure reference voltage and ground
  • Compare APP sensor 1 and 2 voltages at rest and through pedal travel
  • Wiggle test harness while monitoring live data for intermittent changes
  • Check continuity and resistance of wiring between pedal and PCM (with ignition off)

Signal parameters

  • Two independent APP sensor outputs (typically 0.5–4.5 V depending on pedal position)
  • Reference supply usually ~5.0 V and a good chassis/engine ground
  • At idle (pedal released) sensor voltages typically near lower end (≈0.5–1.0 V)
  • As pedal is depressed both sensors should increase (or one increases while the other provides a complementary characteristic) with a linear, correlated relationship
  • Expected correlation tolerance: sensor outputs should track each other across travel; difference usually within ~0.2–0.5 V and correlation coefficient high — large divergence triggers code

Diagnostic algorithm

  1. Connect a capable scan tool. Record freeze frame and live APP sensor 1 & 2 data. Note conditions when fault set.
  2. Visually inspect pedal area, connector, and harness for damage, corrosion, water, or pin pushout. Repair as needed.
  3. With ignition ON (engine OFF), backprobe and verify 5V reference and ground present at the pedal connector. If reference missing, trace to PCM.
  4. Measure both APP sensor output voltages at rest and while an assistant slowly depresses pedal. Verify smooth, monotonic change without dropouts.
  5. Perform a wiggle test on harness and connectors while watching live data to locate intermittent opens/shorts.
  6. Check continuity and resistance between pedal connector and PCM pins with ignition OFF. Repair any opens/shorts.
  7. If wiring and connectors good but outputs out of tolerance or not correlated, replace the APP sensor/pedal assembly and re-test.
  8. If replacement sensor does not clear code, inspect PCM power/ground and input circuits. Consider PCM bench testing or replacement if confirmed faulty.
  9. After repairs clear codes and road-test to confirm fault does not return. Re-scan and verify normal APP correlation.

Likely causes

  • Wiring harness damage (chafing, pinched, rodent chew) between pedal and PCM
  • Corroded or loose connector pins at the pedal or PCM
  • Failed APP sensor assembly
  • Poor 5V reference or ground (feed to APP sensors)
  • Intermittent fault revealed by vibration/wiggle

Fault status

⚠️ Status
PCM detected poor correlation between Accelerator Pedal Position Sensor 1 and Sensor 2 circuits. The discrepancy may trigger limp-home mode and disable cruise control until resolved.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.5 hours

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