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GTECH Calibration
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P1277

Accelerator Pedal Position Sensor 1 Circuit Low Voltage.

  • GM
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
77
FaultThe specific fault in that area

What it means

P1277 on GM vehicles means the engine or powertrain control module has seen the signal voltage from accelerator pedal position sensor 1 fall below its expected range. This usually points to a short to ground, an open circuit on the signal or reference feed, or a fault inside the pedal sensor. The control module cannot trust the driver's pedal demand, so it often limits engine response.

Symptoms

  • Warning light on, often with a reduced engine power message
  • Limited throttle response or engine stuck at a low, fixed idle
  • Poor or delayed acceleration
  • Engine only revs to a limited speed when the pedal is pressed
  • Intermittent loss of power that comes and goes with road bumps or wiring movement

Possible causes

  • Faulty accelerator pedal position sensor assembly (internal track wear or fault)likely
  • Signal circuit shorted to ground or damaged wiring chafing against the bodylikely
  • Open circuit or high resistance in the 5 volt reference feed to the pedal sensorpossible
  • Corroded, loose or spread terminals in the pedal sensor or control module connectorpossible
  • Poor sensor ground connectionpossible
  • Faulty engine or powertrain control modulerare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, then check for other pedal, throttle or 5 volt reference codes that suggest a shared circuit fault
  2. Inspect the pedal sensor connector and wiring for damage, water ingress, corrosion and pushed-back or loose terminals
  3. With a scan tool, watch the pedal position parameters while slowly pressing and releasing the pedal and look for dropouts, jumps or a reading stuck low
  4. Compare pedal sensor 1 and sensor 2 readings, which should track each other smoothly according to the manufacturer's specification
  5. Wiggle the harness and connector with the ignition on and watch for the reading changing or the fault returning
  6. Check the 5 volt reference, signal and ground circuits at the sensor connector against the wiring diagram for your model
  7. Test the signal wire for shorts to ground and the circuits for continuity back to the control module with the module disconnected
  8. Check for related technical bulletins or software updates for your model and engine, as pedal sensor details vary

How to fix

  • Replace the accelerator pedal position sensor assembly if its readings are erratic, stuck low or out of specification
  • Repair or replace damaged wiring where the signal circuit is shorted to ground or the reference or ground is open
  • Clean, repair or replace corroded or loose connector terminals and ensure the connector is fully seated
  • Repair the sensor ground or reference feed if voltage drop is found
  • Replace or reprogram the control module only after all wiring and sensor faults are ruled out and a fault is confirmed in the module, or if an updated calibration is a known fix for your model

Can I keep driving?

Medium severity

The car may be drivable in a limited power mode, but reduced throttle response can be unsafe in traffic or when pulling out of junctions. Get it checked soon and avoid driving if the engine will not respond reliably.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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