Vacuum Decay Test

If the weak vacuum test passes, the PCM will command the EVAP purge valve OFF, sealing the EVAP system. The PCM tests for vacuum decay in the EVAP system by monitoring the Fuel Tank Pressure (FTP) sensor for a change in voltage over a period of time. If the decay rate is more than a calibrated value, the PCM will rerun the test. If the test fails again, DTC P0442 will set.