Faulty accelerator pedal position sensor assembly; Signal wire shorted to the reference voltage or another power supply; Open circuit in the sensor ground wire or a poor ground connection, which pushes the signal high; Corroded, loose or damaged pedal sensor connector terminals; Chafed or damaged wiring harness between the pedal and the control module; Fault inside the powertrain control module.

P1278

Accelerator Pedal Position Sensor 1 Circuit High Voltage.

Chrysler
Powertrain
Manufacturer code
Medium severity

How this code is built

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

What it means

On Chrysler vehicles, P1278 means the powertrain control module has seen the signal voltage from accelerator pedal position sensor 1 sit higher than the expected range. This usually points to a fault in the sensor, its signal wiring, or its reference supply or ground. The module compares sensor 1 against its other pedal sensor, so a high reading can lead it to limit engine power as a safeguard.

Symptoms

Engine warning light on
Reduced engine power or limp mode
Poor or delayed throttle response
High or fixed idle speed
Engine will not rev above a set speed
Cruise control not working

Possible causes

Faulty accelerator pedal position sensor assemblylikely
Signal wire shorted to the reference voltage or another power supplylikely
Open circuit in the sensor ground wire or a poor ground connection, which pushes the signal highlikely
Corroded, loose or damaged pedal sensor connector terminalspossible
Chafed or damaged wiring harness between the pedal and the control modulepossible
Fault inside the powertrain control modulerare

How to diagnose

Read all stored and pending codes and freeze frame data, and note whether other pedal, throttle or reference voltage codes are present
Inspect the pedal sensor connector and harness for damage, water ingress, bent pins and corrosion
Using live data, watch the pedal sensor 1 voltage at rest and while pressing the pedal slowly, and compare it with sensor 2 for smooth, matching movement
With the ignition on and the connector unplugged, check the reference supply and ground against the wiring diagram for your model
Test the signal wire for a short to voltage and the ground wire for continuity and resistance to the module
Wiggle test the harness and connector while watching live data for sudden spikes
If wiring and supplies are good, check the sensor against specification before condemning it
Check for any applicable software updates or technical bulletins for your model, and only consider the module once all else is ruled out

How to fix

Replace the accelerator pedal position sensor assembly if it reads out of range with good supplies
Repair or replace any damaged, shorted or open wiring in the sensor circuit
Clean, repair or replace corroded or loose connector terminals
Restore the sensor ground connection if it is open or high resistance
Replace or reprogram the powertrain control module only if confirmed faulty, or if an outdated calibration is a known cause for your model

Can I keep driving?

Medium severity

The car may still be driveable, but it can drop into reduced power without warning, which is a risk in traffic. Get it checked soon and avoid long journeys or overtaking until it is fixed.

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