Leak Detection Valve: Description and Operation

EVAP CANISTER SHUT-OFF VALVE





Certain markets require the engine control module (ECM) to detect leakages in the tank system, in these markets a leakage diagnostic has been introduced.

In order to check the fuel tank system, cars in these markets have an EVAP Canister Shut-off Valve (5). This is mounted in front of the left A-pillar, inside the front fender and is connected to the EVAP canister opening. The valve is connected to a 12 V supply from the main relay and can be grounded by the engine control module (ECM). The engine control module (ECM) can close the valve by grounding the cable. The EVAP canister shut-off valve valve is normally open, it is only closed when the engine control module (ECM) is checking the system.

Control

Normally the canister purge (CP) valve is closed and only opens when the engine control module (ECM) is emptying the canister. When the EVAP canister is emptied the valve is first pulsed, this pulsing increases to bring the mixture from the canister up to a value which varies according to engine load and speed. Because of the negative pressure in the inlet manifold, fresh air is sucked into the engine through the EVAP canister opening or through the EVAP canister shut-off valve. As the air passes through the EVAP canister, fuel stored in the activated charcoal is drawn into the engine and burned.