Abstract: A system and method for evaluating the integrity of a leak detection test for a purge valve of a fuel system in a vehicle reduces or eliminates false failures. The method is executed on an engine control module (ECM) and is configured to determine when vehicle soak conditions meet first criteria conducive to fuel vapor condensation in the fuel tank. The first criteria include a predetermined temperature drop in ambient air temperature between successive drive cycles. The ECM is further configured to determine when a vehicle maneuver meets second criteria indicative of the capability of the maneuver to initiate fuel slosh in the fuel tank, to thereby establish a trigger event. The ECM is further configured to determine, after the trigger event, the maximum slope of a fuel tank vacuum increase. The ECM is still further configured to produce a slope ratio as a function of the maximum vacuum increase slope and a reference vacuum slope corresponding to a slope that is unaffected by any slosh/condensation events.