What P0318 means
P means powertrain (engine and transmission). The 0 marks a generic code defined by SAE, so the same number means the same thing across makes. The third character, 3, places it in the ignition system or misfire subsystem; the last two digits identify the specific fault.
A rough road surface shakes the drivetrain enough to fool the misfire monitor. Some vehicles use a dedicated rough road sensor (an accelerometer) or wheel speed data to suspend misfire detection on bad roads. These codes cover that hardware.
The letter "A" distinguishes between two or more of the same component on one vehicle. Which physical part is "A" is set by the manufacturer, so confirm it in the service information before replacing anything.
What “Circuit” means here
"Circuit" is the broadest fault type in the standard. The module has found the rough road detection circuit electrically unusable: the signal is missing, outside its electrical limits, or the module's own self-test of the circuit failed. Some vehicles set this instead of the more specific low/high codes; others set it alongside them. Either way the first suspect is the wiring and connector, then the component, and only then the module.
What you may notice
Symptoms depend on the vehicle and on how the module responds to the fault. Any of these can accompany P0318:
- Usually none
- Misfire monitor may not complete
Where to start diagnosing P0318
- Check whether the vehicle should have rough road hardware fitted; a module calibrated for it on a vehicle without it can set this code.
- Inspect the sensor connector and wiring.
- Check related ABS wheel speed codes, as some systems borrow that data.
Clear the code only after recording freeze frame data: it shows the engine speed, load and temperature at the moment the fault set, which is often the best clue to reproducing it.
Live data to watch
These standard OBD2 values relate to P0318. Support varies by vehicle; a value your car does not report will simply be missing.
| Value | What to look for |
|---|---|
| Vehicle speed (PID 0x0D) | Context. |
| Engine RPM (PID 0x0C) | Context. |
Related codes
Codes from the same rough road detection family. If several are stored together, the shared part — wiring, a common reference voltage, or the component itself — is the place to start.
Further reading
Frequently Asked Questions
What does P0318 mean?
P0318 is the generic SAE J2012 code for "Rough Road Sensor "A" Signal Circuit". In plain terms, it means the engine computer has detected a "circuit" fault on the rough road detection.
Can I keep driving with P0318?
Normally drivable; the fault affects diagnostics rather than how the car runs.
What should I check first for P0318?
Check whether the vehicle should have rough road hardware fitted; a module calibrated for it on a vehicle without it can set this code.
Definition source: SAE J2012 / ISO 15031-6 generic DTC definitions. This is the generic meaning that applies across makes; a manufacturer can define a code more narrowly or add its own sub-codes, so confirm against the service information for your vehicle before replacing parts. Written by the OBDAssistant engineering team — see our editorial policy.