What does it mean?
P1277 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: APP Sensor 1 Low Voltage .
Symptoms
- The MIL is on with a reduced power lamp
- The engine idles but does not respond to the pedal at all
- Limp mode with a fixed low rev limit
- Sudden loss of drive on the move while the engine continues to run
- Cruise control inoperative
- Live data shows sensor 1 stuck at or near zero percent regardless of pedal position
Likely causes
- Signal wire shorted to ground or to the sensor ground circuit
- Open circuit on the 5 volt reference feeding sensor 1
- Broken signal wire so the input drops to zero
- Corroded or wet terminals in the pedal connector pulling the signal down
- Internal failure of the sensor track leaving the output at the low end
- Damaged loom under the carpet or at the bulkhead grommet
- Module input circuit fault, only after the wiring has been proven
How to fix it
- Read live data with the ignition on and confirm sensor 1 sits at or near zero while sensor 2 responds normally
- Unplug the pedal connector and measure the 5 volt reference; no reference explains the low signal
- Check the signal wire for a short to ground with the pedal connector and the module connector both disconnected
- With the ignition on, briefly bridge the sensor 1 signal pin to the 5 volt reference pin at the pedal connector; if the reading jumps to full scale the signal wire and the module input are proven good and the fault lies inside the pedal sensor
- Inspect the connector for moisture, corrosion and pushed-back terminals
- Follow the loom for chafing at the bulkhead grommet and under the carpet
- Repair the short or open circuit, or replace the pedal sensor assembly, then complete the learn procedure and confirm the signal sweeps correctly