P0318–P0319 Rough Road Sensor A Signal Circuit
The ECU has logged a fault on P0318. The definition below is the exact wording the standard uses for this code.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P0318 | Rough Road Sensor A Signal Circuit | Investigate soon |
P0319 | Rough Road Sensor B Signal Circuit | Investigate soon |
The definition
P0318: Rough Road Sensor A Signal Circuit.
P0318 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
This one confuses people because on VAG vehicles there is usually no part on the car called a rough road sensor. The ECU needs to know when you are on a bumpy surface so it does not mistake the crankshaft being jolted around for an engine misfire. On VAG that information normally comes from the wheel speed sensors and is sent to the engine ECU over the CAN network by the ABS/ESP controller, rather than from a sensor of its own. The code means that information is missing or implausible, so misfire detection has been suspended. The engine itself is usually running perfectly normally - but while this fault is present a genuine misfire may go unreported, so it is not something to leave indefinitely.
Most likely causes, in order
- A fault in the ABS system or a wheel speed sensor. By far the most common reason, and the one people miss because they only scan the engine. Have every control unit scanned: if there is a wheel speed sensor or ABS controller fault stored alongside, that is your answer, and this code normally stops returning once the ABS fault is repaired.
- CAN communication or coding problem. A missing or wrongly coded control unit, or a damaged CAN wire, means the message simply never arrives. Look for communication faults reported in several modules at once, and think about any control unit that has recently been replaced or retrofitted.
- Genuine sensor or wiring fault where a dedicated sensor is fitted. A few applications do use a sensor of their own for this rather than the ABS data. Establish from your car's own parts and wiring information whether one is actually fitted before going looking for it - on most VAG models it is not.
Worth knowing: Do not go shopping for a rough road sensor. Get a full scan of every control unit rather than just the engine: there is usually an ABS or wheel speed sensor fault sitting alongside this one, and fixing that is what makes this code go away. Clear it afterwards and check it stays away. Fitting parts to the engine on the strength of this code alone is money thrown away.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P0318 mean?
P0318 means Rough Road Sensor A Signal Circuit. It is logged when the ECU sees this circuit outside its expected operating window.
Can I drive with P0318?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.