Single Path Purge Check Valve Diagnostics

Boosted applications use a mechanical check valve between the intake manifold and the Canister Purge Valve (CPV). The purpose of this check valve is to prevent reverse flow through the evaporative emissions system under boosted conditions. The check valve is a simple diaphragm type valve were the rubber diaphragm slides inside a cylinder and is pushed against a stop under boost closing off flow through the valve. While at atmosphere or under vacuum the valve is pulled off the stop allowing flow from the evaporative system to the intake manifold. The check valve diagnostic looks for a failed open, improperly installed, or missing valve that could result in intake manifold vapors being pushed back into the evaporative emissions system (see figure below). A failed check valve is detected if the rate of rise in Fuel Tank Pressure Sensor is greater than a calibratable threshold while the Canister Vent Valve is closed, Canister Purge Valve open, and the engine is boosted above a minimum level (under boost the system should be sealed if the check valve is operating properly). This condition will set DTC P144C.

System schematic showing the potential for reverse flow if the check valve is failed.

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