تسرب في نظام التبخير

A leak anywhere in the sealed evaporative system, which the monitor detects by pressurising or evacuating the tank and watching it fail to hold. The code reports the leak's approximate size and not its position, which is the whole difficulty — the system spans the tank, the canister, the valves and metres of line under the vehicle.

Size narrows the search usefully. A gross leak is a disconnected hose, an open cap or a broken canister spigot and is usually found by looking; a very small leak is a seal, a hairline crack or a valve not quite closing and will never be found by inspection.

Smoke testing is the only reliable method for the small ones, introducing vapour under low pressure and watching where it escapes. Start at the cap and its seal, which is the commonest single cause and free to check. Note that the monitor only runs under specific conditions — a particular fuel level, temperature and soak time — which is why the code can be intermittent while the leak is constant.