Saab 9000 - Page 81

78 Technical Description
Fault crite·ria, EVAP M96
Diagnosis is carried out once per trip and its purpose
is to determine whether the electronic 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 ob-
tained 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 conti-
nues by stopping regular purging.
Closed loop and idle speed control mean values are
then stored in the memory.
A.%
EVAPo/o ..._ ___
2
5,6 7
3,__ _ ___.
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 en-
ough, the fault criteria are satisfied.
The electrical circuit of the valve is also monitored
continuously in accordance with the On-BoardDiag-
nostics I model.
Condttlons for diagnosis
• Diagnosis not yet performed this trip
• Transition diagnosis of front heated oxygen sensor
OK
• Vehicle speed
=
O
• Idling speed
• No load changes
• Purge valve active
• Steady idling speed
Saab 9000
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