P0318 code meaning
Rough Road Sensor A Signal Circuit
What P0318 means
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.
P0318 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0318
- Service message (GM without warning light)
- Often ABS or stability warning at the same time
- Driving unaffected
Common causes of P0318
- Most likelyWheel speed sensor or wiring faulty – the brake module passes on the fault
- PossibleCommunication between engine and brake module lost (CAN, connector, supply)
- Less likelyBrake control module faulty
- Less likelySeparate rough-road sensor faulty, where fitted
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Wheel speed sensorsABS moduleCAN bus
What each part of P0318 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 3 | Area: ignition system or misfire. |
| 18 | The exact fault in that area. |
What to do next
- Note P0318 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0318
What does P0318 mean?
P0318 means "Rough Road Sensor A Signal Circuit". Misfire detection works from crankshaft speed fluctuations, which rough roads also cause. It is a generic code, so it means the same on every make.
Is it safe to drive with P0318?
P0318 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will P0318 fail an emissions test?
P0318 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is P0318 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0318 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.