Purge Valve

It sits in the line between the charcoal canister and the intake manifold. The control unit opens it when the engine is warm and running, so vapour is drawn in and burnt. A valve stuck open lets vapour in all the time, which can cause rough idle after refuelling and hard starts. A valve stuck closed lets the canister fill up.

The valve is usually located on or near the intake manifold and is connected to the canister by a hose. Purge flow is usually highest once the engine is warm and running at part load. Because the purge valve introduces extra fuel into the intake, the control unit watches the fuel trims and oxygen sensor closely while purging, reducing injection so that the mixture stays correct.

The solenoid valve is pulsed open by the control unit. The amount of vapour is taken into account through fuel trim. The control unit opens it in pulses when the engine is warm and running, and adjusts fuel injection to account for the vapour.

Purge valve faults set EVAP codes such as P0496 or P0441 and may cause a fuel smell or hard starting right after a fill-up. A valve stuck open can cause rough idle and hard starting after refuelling; one stuck closed can set EVAP codes. Testing it is quick with a scan tool or vacuum pump.