What does it mean?
P1633 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Acceleration Pedal Position Sensor 2 Signal Too Low .
Symptoms
- MIL (check engine lamp) on with a reduced power warning
- Engine restricted to a low rpm ceiling, with the module falling back on the remaining pedal channel
- Sluggish or delayed acceleration, hesitation at part throttle
- Sudden power loss during driving that clears after a restart
- Cruise control unavailable
- Unstable idle in some cases
Likely causes
- Open circuit or short to ground on the sensor 2 signal wire
- Loss of the reference voltage supplied to the second sensor channel
- Water and corrosion in the accelerator pedal connector affecting only one channel
- Worn or contaminated sensor 2 track inside the pedal module
- Harness chafed or pinched under the carpet or where it passes through the bulkhead
- Pedal assembly mechanically damaged or obstructed
- Module input circuit fault, the least likely cause
How to fix it
- Graph both pedal channels together in live data during a slow full pedal sweep; sensor 2 should follow its own smooth curve without dropouts
- Wiggle the pedal harness and connector while watching channel 2 for glitches
- Measure the reference voltage and ground for the second channel at the pedal connector
- With the connectors unplugged, test the sensor 2 signal wire for continuity and a short to ground
- Inspect the footwell and the connector for moisture, corrosion and previous repairs
- Replace the accelerator pedal assembly when the channel 2 track is proven faulty
- Perform the pedal learn procedure and confirm both channels agree over the full range