P0318Rough Road Sensor A Signal Circuit
- Generic OBD-II code · Powertrain
- How the car detects it
- Misfire detection works from crankshaft speed fluctuations, which rough roads also cause. CARB therefore allows misfire detection to pause on rough roads; many engines take a rough-road signal from the wheel speeds of the ABS module, a Ford patent describes such a detector. P0318 means rough-road signal A is missing or invalid. On GM engines (documented in Saab service information for the 1.6 turbo) the brake control module sends wheel speed over the data bus; the code sets between 1,520 and 4,000 rpm when that module reports a wheel speed sensor fault or no signal arrives for more than 5 s. GM files it without the warning light. Misfire detection then runs without its rough-road filter. ABS or stability warnings and further codes often appear at the same time.
- What you may notice
- Service message (GM without warning light)
- Often ABS or stability warning at the same time
- Driving unaffected
- Likely causes
- LikelyWheel speed sensor or wiring faulty – the brake module passes on the fault
- PossibleCommunication between engine and brake module lost (CAN, connector, supply)
- RareBrake control module faulty
- RareSeparate rough-road sensor faulty, where fitted
- Repair
- Medium · Often possible to do yourself.Typical cost: €50 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.