may occur the processor directs pump 119 at step 204 to run until the pressure sensed by the pressure sensor equals a preselected target pressure p 1 alternatively to conduct a vacuum leak detection test the processor would direct the system to evacuate to a negative pressure via actuation of normally closed canister purge valve 115 the processor therefore should sample the pressure reading with sufficient frequency such that it can turn off the pump 119 or close valve 115 before the target pressure p 1 has been significantly exceeded at step 206 which should occur very close in time to step 204 the processor samples and in the memory records the fuel vapor temperature signal t 1 generated by the temperature sensor the processor at step 208 then waits a preselected period of time e g between 10 and 30 seconds when the desired amount of time has elapsed the processor at step 210 samples and records in memory the fuel vapor temperature signal t 2 as well as fuel vapor pressure p 2 the processor at step 212 then computes an estimated temperature compensated or corrected pressure p c compensating for the contribution to the pressure change from p 1 to p 2 attributable to any temperature change t 2 t 1 in an embodiment of the present invention the temperature compensated or corrected pressure p c is computed according to the relation and the result is stored in memory finally at step 214 the temperature compensated pressure p c is compared by the processor with the nominal pressure p 2 if p 2 is less than.