Fault criteria, evaporative emission system
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Fault criteria, evaporative emission system
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The diagnosis was improved for M97 and further improved for M98 with a view to preventing Check Engine going on when there was no fault present. M98 was principally modified so that diagnosis was permitted twice during the same driving cycle if the coolant temperature was below 40C (104F) when the engine was started. Both the cold starting diagnosis and the ordinary diagnosis must be performed and a leak indicated on both occasions before a diagnostic trouble code can be generated. Diagnosis for M99 is unchanged.
The diagnosis is performed once each trip and is used to determine whether there is a leak corresponding to a hole of diameter 1 mm (0.040”) in the evaporative emission system.
The system includes a tank pressure sensor and a close valve for the air supply to the EVAP canister.
When the conditions for the diagnosis have been fulfilled and the air supply to the EVAP canister has been stopped, the EVAP canister purge valve should be able to control the tank pressure.
The diagnosis starts by storing the value from the tank pressure sensor.
Then, the PWM ratio of the purge valve is set to 15% and the EVAP close valve closes. The purge is interrupted when the tank pressure has dropped by 0.6 kPa.
The rate at which the tank pressure increases is now monitored.
Fault criteria are fulfilled if a drop in pressure of 0.6 kPa cannot be obtained within 23 sec. or if the tank pressure rises by more than 0.3 kPa for 9 sec. after the purge ceased. If the cold start diagnosis indicates a leak, the close valve will be activated 4 times in rapid succession to remove any impurities from the valve sealing surfaces.
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Diagnosis not yet performed during this driving cycle.
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No fault on oxygen sensor 1
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Diagnosis commenced less than 8 times during this driving cycle.
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Approved transition diagnosis of oxygen sensor 1.
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Vehicle speed = 0 for 7 sec.
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Car stationary for more than 5 sec.
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Max. one change of status of the brake light switch.
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The purge valve PWM has exceeded 40 % at some time
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Additional fuel from purge <7 % of that required by engine
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If the diagnosis is interrupted, the vehicle speed must exceed 4 km/h (2.5 mph) on one occasion before the diagnosis can be restarted.
While a diagnosis is in progress, the PWM of the purge valve will be set to 15 % at the same time as the additional fuel from the purge is allowed to be 13 % of that required by the engine.
If the cold start diagnosis indicates a leak, the close valve will be activated 4 times in rapid succession to remove any impurities present on the sealing surfaces of the valve.
The cold start diagnosis can be initiated with the diagnostic tool irrespective of the coolant temperature when the engine was started. At high temperatures and when the EVAP canister is saturated, it may be difficult to carry out the diagnosis as the additional fuel from the purge is then often more than 7 % of the engine's fuel requirements.
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1.
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Store reference value:
-tank pressure
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2.
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Close EVAP canister close valve
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3.
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Tank pressure drops > 0.6 kPa within 23 sec.
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4.
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Interrupt ordinary purge
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5.
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Tank pressure rises < 0.3 kPa for 9 sec.
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6.
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Diagnosis performed during this trip. Return to ordinary purge
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7.
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Fault criteria for evaporative emission system fulfilled
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