Code
P1272
HUMMER
P — Powertrain
Accelerator Pedal Position Sensor 2
AI status
Completed
Completed
100%
Causes
- Damaged, corroded, or disconnected pedal sensor connector
- Broken, shorted, or intermittent wiring between pedal and ECM
- Failed accelerator pedal position sensor (sensor 2)
- Contaminated or mechanically damaged pedal assembly
- ECM input or ground fault (less common)
- Software/firmware issue or required relearn/calibration
Symptoms
- Check Engine MIL illuminated (DTC P1272 stored)
- Limp-home / reduced engine power or poor throttle response
- Hesitation, delayed throttle response or surging
- Cruise control may be disabled
- Possible inability to start (in some control strategies) or abnormal idle
What to check
- Retrieve DTC(s) and freeze-frame data with a scan tool; record live APP1 and APP2 values
- Perform a visual inspection of the accelerator pedal assembly, connector and wiring harness for damage, corrosion, or water intrusion
- Verify battery voltage and good chassis/engine ground before testing
- Backprobe pedal connector and measure reference voltage (typically ~5 V) and ground presence with key ON (engine off)
- Measure APP2 signal voltage at rest and during pedal travel; compare to APP1 and manufacturer specifications
- Perform wiggle test on wiring and connector while monitoring live data for intermittent faults
Signal parameters
- Reference (supply) voltage: typically ~5.0 V (manufacturer-specific tolerance ±0.5 V)
- Ground: solid low-resistance reference to vehicle ground
- Signal voltage: typically varies across pedal travel in the approximate 0.2–4.8 V range (exact values depend on design)
- APP1 and APP2 must change smoothly with pedal travel and correlate per manufacturer (may be complementary or matching curves)
- Expected behavior: no sudden jumps, dropouts, excessive noise, or stuck values; both sensors should be steady with foot off pedal
Diagnostic algorithm
- Safety: Park vehicle, apply parking brake, key OFF. Use manufacturer procedures for testing live sensors.
- Retrieve and record all stored codes, freeze-frame and live APP1/APP2 data with a scan tool.
- Visually inspect pedal, connector, and wiring for damage, corrosion, water entry, or pin deformation. Repair as needed.
- With key ON (engine off), backprobe connector: verify reference voltage (~5 V) and ground present. If reference missing or out of range, trace/repair short or open to power.
- Measure APP2 signal voltage at rest and while slowly pressing the pedal. Confirm smooth change and that values fall within expected manufacturer range. Compare to APP1; verify correlation (both should follow expected relationship).
- Wiggle harness and connector while monitoring APP2 to find intermittent faults. Repair any broken wires or poor connections.
- If reference and ground are good but signal is out-of-range, noisy, or does not change, suspect a failed APP2 sensor—replace pedal assembly or sensor per service manual.
- If wiring and sensor check good, inspect ECM connector and ground circuits. Perform continuity/short-to-ground tests on suspect circuits.
- After repair or replacement, clear codes, perform any required throttle/pedal relearn/calibration per manufacturer, then road test to ensure code does not return.
- If problem persists after wiring and sensor replacement, consider ECM fault and consult manufacturer diagnostics or test ECM inputs.
Likely causes
- Open or short in APP2 signal, reference (5 V) or ground circuit
- Corrosion or poor pin contact at pedal connector
- Internal failure of APP sensor 2 (out-of-range or noisy output)
- Misalignment or mechanical interference with pedal travel
- Intermittent wiring due to chafing/movement
- ECM hardware fault or missing throttle body/pedal relearn
Fault status
Status
P1272 — Accelerator Pedal Position Sensor 2 Circuit/Performance (HUMMER): APP2 signal out of range, implausible, or not correlating with APP1.
Repair difficulty: Medium
Diagnostic time: 0.5–2.0 hours
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Repair manuals
Manual library for HUMMER
138
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