Evaporative Purge System Monitoring

Schematic Evaporative System





Tables of OBD Requirements for Evaporative Purge System Monitoring

General Description

The purge flow from the charcoal canister through the purge valve is monitored after fuel system adaption is completed and the lambda controller is at closed loop condition. The diagnosis is started during regular purging.





Monitoring Structure

Step 1 - For rich or lean mixture

Flow through the purge valve is assumed as soon as the lambda controller is compensating for a rich or a lean shift.
After this procedure the diagnosis is completed and the evaporative purge system resumes working normally.

Step 2 - For a stoichiometric mixture

In this case the lambda controller does not need to compensate for a deviation. Therefore, after finishing the regular purging, the purge valve is opened and closed abrupt for several times. The effect of additional cylinder charge triggers by a variation of the engine idle speed.

A predetermined value is reached if the system functions properly and the diagnosis procedure is completed.

To start the diagnosis function (step 2) several conditions have to be satisfied.
- vehicle speed 0
- engine at idle speed
- closed loop of lambda controller
- coolant temperature 97°C
- air conditioning system not active at the time
- transmission in gear position, not "P" or "N"

Furthermore if the diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted and started again later.

- no throttle position change
- engine idle speed variation = 560 < n < 720 (rpm)
- engine load variation = 1.3 < TL < 1.8 (ms)
- steering wheel rotary motion = < 5°