Detecting leaks in the EVAP system
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SERVICE INFORMATION
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Bulletin Nbr:
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234-1746
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Date:
...........
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MARCH 1997
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Market:
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US ONLY
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Detecting leaks in the EVAP system
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Saab 900 M96-97 with EVAP II.
It is possible for spurious diagnostic trouble codes relating to leaks in the EVAP
system to occur. A method has therefore been developed for checking whether a code is
spurious or whether there really is a leak in the EVAP system.
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1.
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Check that the pressure tester is in good
condition and not leaking.
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2.
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Check that the filler cap is on tight.
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3.
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Using e.g. a ’T’ piece, connect pressure tester J41413
between the inlet on the EVAP canister purge valve and the hose.
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Note
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Do not fit the pressure tester adaptor to the filler cap connection, as this would prevent
the filler cap from sealing in its normal position.
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4.
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Activate the EVAP canister shut-off valve by connecting battery voltage to the
valve (male connector on M96).
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5.
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Pressurize the system and perform the pressure test, following the instructions in
the Kent-Moore manual.
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Action to be taken if leak detected
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1.
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Ensure that the shut-off valve is still
energized.
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2.
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Disconnect the hose from the EVAP canister purge valve at the intake
manifold.
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3.
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Raise the pressure again, following the instructions in the Kent-Moore
manual.
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4.
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Use ultrasonic leak detector J41416 to trace the leak. Start with the hose that
has been disconnected from the intake manifold and then follow the system lines and
components. Make a visual check of the system at the same time.
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Note
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The ultrasonic leak detector is sensitive to ambient noise in the workshop, such as that
made by exhaust-extraction equipment, compressors, air guns, air leaks from pneumatic
equipment, etc.
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Air flows from the ventilation equipment in the workshop can also create interference to
the ultrasonic detector.
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All such noise and interference can give rise to spurious readings indicating leaks in the
EVAP system, even when there are none.
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Always, therefore, adjust the sensitivity of the ultrasonic leak detector, so that
the ambient noise, which often causes interference, is filtered out.
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Note
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Major leaks, such as those caused by a defective canister shut-off valve or a loose
hose connection, are difficult to detect, as the noise generated by them is usually outside the
sensitivity range of the ultrasonic detector.
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For this reason, it is essential that you make a thorough visual inspection of the system
components, to check for leaks not detected by the equipment.
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If you suspect leakage from the EVAP canister (located on the inside of the RH front
fender/wing) or its connections, this can be easily checked. Remove the side direction
indicator and insert the microphone there.
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5.
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Rectify any leaks detected and test the system again.
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6.
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Restore the car to its normal condition.
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