Fault Criteria, Fuel Evaporation M96

Diagnosis is carried out once per trip and its purpose is to determine whether the engine control module can control a flow through the purge valve.

Closed loop or idle speed control should be affected when the conditions for diagnosis are fulfilled and the purge valve is activated.

Diagnosis starts by checking the additional fuel obtained from the purging process., If the additional fuel is more than 10%, the result of the diagnosis is OK If the additional fuel is less than 10%, diagnosis continues by stopping regular purging.

Closed loop and idle speed control mean values are then stored in the memory.

Purging starts and the pulse ratio is increased until a sufficient change in the closed loop or idle speed control can be observed.

If no change is large enough, it is assumed that the purging flow contains no hydrocarbons and that idle speed control has been disturbed.

A new reference value for idle speed control is now stored in the memory.

Purging is interrupted and the change in idle speed control observed. If the change is still not large enough, the fault criteria are satisfied.

The electrical circuit of the valve is also monitored continuously in accordance with the On-Board Diagnostics I model.

Conditions For Diagnosis
^ Diagnosis not yet performed this trip
^ Transition diagnosis of front heated oxygen sensor OK
^ Vehicle speed = 0
^ Idling speed
^ No load changes
^ Purge valve active
^ Steady idling speed