EVAP System, Diagnostic Leak Test
- Observe safety precautions.
- Observe rules of cleanliness.
NOTES
- Replacement hose clamps must be the same type of clamp that was used in production See parts catalog microfiche..
- When reassembling, always replace O-rings and seals.
Test requirements
- DTC memory checked
- All electrical consumers switched off (engine cooling fan must NOT run during test)
- A/C switched off
- Intake Air Temperature (IAT) less than 90 °C (194 °F) See display group 004, display field 4.
- Engine coolant temperature less than 95 °C (203 °F) See display group 004, display field 3.
- Throttle valve angle less than 10° See display group 003, display field 3.
- Connect VAG 1551 or VAG 1552 scan tool with diagnostic cable VAG 1551/3. Refer to On-Board Diagnostics II in Computers and Control Systems/System Diagnosis. Testing and Inspection
- Start engine and let it idle.
- Press button -1- for "Rapid data transfer" operating mode 1.
Indicated on display
Rapid data transfer HELP
Insert address word XX
- Press buttons -0- and -1- to insert "Engine Electronics" address word 01 and press -Q- button to confirm input.
Indicated on display
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08 and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block HELP
Input display group number XXX
- Press buttons -0-, -7- and -1- to input display group number "071" and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block ->
Reed cl Abort Test ON
NOTES:
- if "Reed Cl" (closed) is displayed, then continue the test.
- "Abort" does not always appear on the display.
- if the display shows "Reed open", briefly open and close the fuel filler cap to release pressure. This should close the reed contact. Continue the test as follows:
- Press buttons -0- and -4- to select "Basic Setting" function 04.
Indicated on display
System in Basic Setting 71 ->
Reed open Test ON
The Evaporative Emission (EVAP) canister purge regulator valve will open to initiate a pressure release (purging) of the system. Then the Leak Detection Pump (LDP) -V144- will trigger. This operation takes about 60 seconds.
Indicated on display "Test on"
System in Basic Setting 71 ->
Reed open Syst. Test Test ON
The system test will begin automatically. At the end, the Leak Detection Pump (LDP) -V144- will start to run. The pump will switch off when the pumping time has run out.
The process take about 60 seconds.
Indicated on display
System in Basic Seting 71 ->
Reed open Check Test ON
The measuring phase begins. The LDP is switched off and the Engine Control Module (ECM) checks the Motronic system to see if the reed contact closes within 10 seconds.
If the reed contact does not close within the 10 second test period:
Indicated on display
System in Basic Setting 71 ->
Reed open Check END Syst. OK
The system is OK, no leaks were detected, the test is ended.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
If the reed contact closes within the 10 second test period:
The Leak Detection Pump (LDP) -V144- will pump 4 strokes for an additional test. The Engine Control Module (ECM) monitors the time it takes to perform the strokes until the reed contact closes again.
Indicated on display
System in Basic Setting 71 ->
Reed Leak END Syst.n.OK
The system has detected a leak that is smaller than 1 mm (0.039 in.) in diameter.
Indicated on display
System in Basic Setting 71 ->
Reed cl Lg. Leak END Syst.n.OK
The system has detected a leak that is larger than 1 mm (0.039 in.) in diameter.
- If system has detected small or large leak, check fuel supply system and tank ventilation systems for leaks and repair as necessary.
- After repairs are completed, repeat leak test.
Checking fuel supply and ventilation systems for leaks
NOTE: The following describes areas in the fuel supply and ventilation systems that should be checked for possible leaks. After making the necessary repairs, carry out the leak test again to make sure that all of the leaks were successfully repaired.
- Switch ignition off.
- Check to make sure fuel filler cap was tightly closed.
- Check seal of fuel filler cap for damage. Replace if necessary.
- Check to make sure seals under closing flanges are light.
- Check to make sure all fuel line connections are OK and union nuts are properly tightened.
Front-wheel drive vehicles
- Remove cover for closing flange under luggage compartment liner.
All-wheel drive vehicles
- To remove rear closing flange, remove luggage compartment liner and remove cover for closing flange.
- To remove front closing flanges, remove rear seat bench and remove covers for closing flanges.
All vehicles
NOTE: Follow the installation instructions for closing flanges:
- Visually inspect all lines and connections of fuel supply system and repair leaks by replacing, for example:
- Line from Evaporative Emission (EVAP) canister purge regulator valve in engine compartment
- Lines from EVAP canister to Leak Detection Pump (LDP) (under wheelhousing liner, at right-rear)
- Line from fuel tank to EVAP canister (under cover for EVAP canister)
- Fuel system ventilation lines under left-rear wheelhousing liner
- Fuel supply lines to engine
NOTE: Using a commercially available leak detection spray may be helpful to detect leaks at lines and components of the fuel supply system. After applying the spray, initiate the leak detection diagnosis to increase pressure in the system. Leaks should be visible by bubbles forming at the leak.
CAUTION! Make sure that the leak detection spray is designed to be used for fuel systems. The spray must not be flammable, must not contain silicone or silicone compounds and must be safe to be used in confined spaces.
- Visually inspect components of fuel supply and ventilation systems:
- Fuel tank
- EVAP canister
- Leak Detection Pump (LDP)
- Evaporative Emission (EVAP) canister purge regulator valve -N80-
NOTES:
- Because of the shape or function of these components it is not always possible to find leaks by applying spray. It may be necessary to close off the component using 3093 hose clamps and initiate the leak detection diagnosis. If the leak stops, replace the component that was clamped off
- If the LDP itself is clamped off and there is still a leak, then the LDP itself is leaking.