EVAP System - Leak Detection
SI No. 234-1746PI No.
Date: October 1997
Distr. US only
900
Detecting leaks in the EVAP system
Cars concerned
Saab 900 M96-98 with enhanced EVAP system
(900 Turbo and 900 V6 models)
Background
In October 1997 Saab is introducing a new essential special tool. This test equipment, Kent-Moore J41413 "Pressure/Purge Diagnostic Station" is designed to diagnose leaks in any EVAP system, but is especially useful when troubleshooting Diagnostic Trouble Codes P0442 and P0455 on M96 and later engine management systems with enhanced EVAP.
During October, 1997 Saab will issue a video and self-study workbook which technicians can complete at the dealership. The video and workbook will include a review of the enhanced EVAP system used on some M96 and later models, an overview of the On-Board Refueling Vapor Recovery System introduced on M98 900 models, and an introduction to the use of the Kent-Moore J41413 "Pressure/Purge Diagnostic Station".
Should you require help using this equipment or have any questions concerning its use, please call the Technical Assistance Center at 1-800-766-2857.
An updated bulletin with more detailed information regarding the use of this equipment will be issued shortly.
NOTE:
The Kent-Moore J41413 "Pressure/Purge Diagnostic Station" requires a tank of nitrogen gas for operation. You can usually lease a tank of nitrogen from the same supplier you use for oxygen, acetylene, or welding supplies. A 125 cu.ft. or 150 cu.ft. tank is probably the most convenient size to use on the J41413.
Checking for leaks
If you are diagnosing DTC P0442 (small EVAP leak), P0445 (large EVAP leak). or if you have a customer complaint of fuel odors, follow this procedure:
1 Perform a "self-test" of the J41413 test station according to the instructions included with the test station.
2 The test station can be connected by using a gas cap adapter or a "test port". We recommend that you leave the gas cap in place whenever possible. For this reason, a "test port" is included with the test station.
3 Disconnect the hose from the EVAP purge valve to the charcoal canister (usually at the rear of the EVAP purge valve). Using a short piece of hose, temporarily connect the "test port" between this hose and the EVAP purge valve. Connect the red hose from the test station to this "test port".
4 Activate the Canister Close Valve. On M96 and M97 models, this must be done with a jumper wire as explained in PSI 01/97-0729 (Section 2, p. 61). On M9B 900 Turbo models, use TECH 2 "Activate/Canister Close Valve" command.
5 With the engine NOT RUNNING, turn the control knob on the test station to the "Pressure" position to pressurize the system to 5 inches of water. If the system cannot be pressurized to 5 inches of water, you have a large leak.
6 If the system can be pressurized to 5 inches of water, continue to pressurize to 15 inches of water. Turn the control knob to the "Off/Hold" position. System pressure should not drop below 8 inches of water within 2 minutes. If it does, you have a leak.
Action to be taken if leak detected
1 Ensure that the canister close valve is still energized.
2 Leave the red hose from the test station connected to the "test port".
3 Turn the control knob to the "Pressure" position to ensure that nitrogen is flowing.
4 Use ultrasonic leak detector J41416 to trace the leak. Follow the system lines and components. Make a visual check of the system at the same time.
Note
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. Air flows from the ventilation equipment in the workshop can also create interference to the ultrasonic detector.
All such noise and interference can give rise to spurious readings indicating leaks in the EVAP system, even when there are none.
Always, therefore, adjust the sensitivity of the ultrasonic leak detector, so that the ambient noise, which often causes interference, is filtered out.
Note
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.
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.
If you suspect leakage from the EVAP canister on M96 and M97 models, it is located on the inside of the RH front fender. This can easily be checked by removing the side direction indicator and inserting the ultrasonic leak detector there. On M98 900 models, the canister is below the vehicle, behind the gas tank.
5 Rectify any leaks detected and test the system again.
6 Restore the car to its normal condition.