Leak Test Operation

Leak Test Operation.
The leak test will be initialised when a number of entry conditions are satisfied. They will include engine coolant temperature, intake air temperature, engine load, vehicle speed, vapour concentration and purge amount.

40 thou Leak Test.
When the entry conditions are satisfied the purge valve will be closed and the canister closure valve (CCV) will then close, the evaporative system is now sealed, the fuel tank pressure sensor (FTPS) will take the initial value of pressure (P1), after 15 seconds the FTPS will take a further reading (P2), the difference between the two becomes the 1st pressure rise.

The purge valve will then be ramped open to pull the FTP down to -2.00kpa; the purge valve will then close. If the pressure rises too quickly then a second pull down will occur. The FTPS then takes a reading of tank pressure (P3), after a further 15 seconds a final pressure reading (P4) is taken and the difference between these two readings will then become the 2nd pressure rise.

The CCV is opened and the leak value is calculated and compared with the pass / fail threshold. The result may be discarded if the vapour concentration is too high, the first pressure rise is too high or the fuel movement in the tank causes excessive vapour. If the pressure in the tank does not return close to atmospheric within a few seconds of the CCV opening then the test will continue and may flag DTC P0446.

If when the purge valve is ramped open the tank is not pulled down to -2.00kpa a gross leak will be flagged P0455 unless in the 2nd pressure rise the tank pressure rises to a value, which would indicate that it couldn't be a gross leak.

Failure to pull the tank pressure down resulting in flagging P0455 can be due to a gross leak, vapour pipe detached/fuel cap left off etc. Or purge valve stuck closed or CCV stuck open.

Leak Test Diagram 40 thou Test.






20 thou Leak Test.
The 20 thou Leak Test is similar to the diagram above, with the exception that the tank is pulled down to -1.25 kPa rather than -2.00 kPa as above. In addition the 20 thou test is carried out at idle or with the vehicle moving at less then 15kph. Component faults P0443, P0446, P0450 & P0455 cannot be determined from the 20 thou test.