Evaporative Emission (EVAP) System, Diagnostic Leak Test
Evaporative Emission (EVAP) System, Diagnostic Leak Test
Special tools and equipment
- VAS 5051
- Observe safety precautions
- Observe rules for cleanliness
NOTE:
- All hose connections are secured with clips.
- Always replace seals and gaskets.
Requirements
- Parking brake engaged.
- Vehicles with manual transmission: shift lever in neutral.
- Vehicles with automatic transmission: selector lever in P or N.
- Engine is running at idle
- Electrical consumers switched off (coolant fan must NOT run during test)
- A/C switched off
- VAS 5051 tester connected and -"01 Engine electrical" selected.
- No DTCs in DTC memory
- Intake Air Temperature (IAT) less than 90 degrees C => display group 004, display field 4
- Coolant Temperature less than 95 degrees C => display group 004, display field 3
- Throttle valve angle less than 10 degrees % display group 003, display field 3
Work sequence
Display on VAS 5051:
- In selection -1-, click on diagnostic function "04 - Basic setting".
Display on VAS 5051:
1 - Enter display group
- Select function "071" in button field -2- for "display group number 071" and press Q button to confirm input.
Display on VAS 5051:
- Check indication in display field 1.
- Specification: "Reed closed"
NOTE:
- If "Reed cl" (closed) is displayed, continue test.
- If display indicates "Reed open": briefly open and close fuel filler cap to release pressure from fuel tank. This will close the reed contact.
- Activate basic setting by pressing button A.
- Check indication in display field 4.
- Specification: "Test ON"
The system test lasts several minutes.
- Check indication in display field 4.
- Specification: "System OK"
System is sealed, test is terminated.
- End function "04 - Basic setting" by pressing <- button.
DTC display
If a DTC is recognized during the system test, the DTC evaluation follows.
On VAS 5051 display in display field -4-:
- In case of malfunction: System not OK
- Check diagnosis evaluation in display field -2-.
- "Small leak" or "large leak"
- End function "04 - Basic setting" by pressing <- button.
If the system recognizes a small or large leak:
- Checking fuel supply and ventilation systems for leaks
- After that, 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 necessary repairs, perform leak test again to ensure that all leaks were successfully repaired.
- Switch ignition off.
- Check whether fuel filler cap was completely closed for test.
- Check seal of fuel filler cap for damage. Replace if necessary.
TT Coupe
- Remove rear seat bench.
Vehicles with Front Wheel Drive (FWD)
TT Roadster
- Remove rear panel side trim.
- Unscrew cover -1- at right (arrows).
Vehicles with All Wheel Drive (AWD)
TT Roadster
- Remove rear panel side trim.
- Unscrew cover -1- at right (arrows).
Continued for all vehicles
- Check whether seals under connection flanges are OK and union nuts are properly tightened. Also check fuel line connections.
NOTE: Observe installation notes for connector flanges
- Visually check all wires and hose connections of fuel supply system and replace loose lines, e.g.:
- Line from EVAP canister to Evaporative Emission (EVAP) Canister Purge Regulator Valve -N80 (in engine compartment)
- Lines from EVAP canister to Leak Detection Pump (under front right wheelhousing liner)
- Line from fuel tank to Evaporative Emission (EVAP) canister (under cover for EVAP canister)
- Lines from EVAP system (under right wheelhousing liner)
- Fuel lines to engine
NOTE: Leaks at lines and components of fuel supply system can sometimes be located using a non-flammable, environmentally sound leak detection spray. For this, initiate leak testing several times in sequence to build pressure in the system. Leaks can be detected via bubbles forming at the leak.
- Visually check components of fuel supply system and EVAP system.
- Fuel tank
- EVAP canister
- Leak Detection Pump (LDP) -V144-
- Evaporative Emission (EVAP) canister purge regulator valve -N80-
- Evaporative Emission (EVAP) canister purge solenoid valve -N115-
NOTE:
- 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 clamp off the relevant component using 3094 hose clamps and initiate the leak detection diagnostic. If the leak is no longer detected, the component that was clamped off is faulty. If the clamp is placed directly on the diagnostic pump and a leak is still detected, then the diagnostic pump itself is leaking.
- Checking Evaporative Emission (EVAP) canister purge regulator valve -N80-
- For leaking Evaporative Emission (EVAP) canister purge solenoid valve -N115-, replace O-rings
Work sequence
- Ignition on
- VAS 5051 tester connected and "01 Engine electrical" selected.
Checking function
Display on VAS 5051:
- Click on diagnostic function -1- "03 Output check diagnosis"
- Click -> button until leak detection pump begins functioning.