With Manufacturer's Scan Tool

Evaporative Emission (EVAP) system, checking for leaks

Special tools and equipment

- VAG 1551 Scan Tool

Note: The VAG 1552 vehicle system tester can be used instead of the VAG 1551 Scan Tool, however a print-out is not possible.

- VAG 1551/3 Cable

Test conditions

- Fuse No. 43 must be OK
- No malfunction stored in DTC memory
- All electrical consumers, e g. lights and rear window defroster must be switched off
- If the vehicle is equipped with an air conditioner, this must be switched off
- Throttle valve angle less than 4 1%=display group 03, display zone 3
- Coolant temperature less than 95° Display group 04, display zone 3
- Intake air temperature less than 90° Display group 04, display zone 4

Functional check
- Connect VAG 1551 Scan Tool (or VAG 1552 Scan Tool). Start engine and select Engine Control Module with "Address word" 01.
Connecting scan tool and selecting Engine Control Module:

Indicated on display
- Press buttons -0- and -8- for function "Read Measuring Value Block" and confirm entry with -Q- button.

Indicated on display
- Press buttons -0-, -7- and -1- for "Display group number 71" and confirm entry with -Q- button.

Indicated on display

- Check display in display zone 1:

If "Reed open" appears in display group 1:
- Open fuel tank cap briefly to allow pressure in fuel tank to dissipate, this will close reed contact.

If the specification is obtained:
- Press button 4 for "Introduction of basic setting" function.

Indicated on display
The test of the Evaporative Emission (EVAP) system will be initiated. First of all the function of the Reed contact (in the Leak detection pump - V144) will be checked by the control module.
After approximately 10 seconds the Leak Detection Pump (LDP) -V144- will be activated and build-up pressure in the fuel system.

Indicated on display
The test will be initiated after approximately 50 seconds (when there is sufficient pressure available in the fuel system can last up to 120 seconds).

Indicated on display
The Leak detection pump V144- switches off and the control module measures the time until the reed contact closes.

Indicated on display

- Check display in display zones 3 and 4: specified value display field 3:
Check.END Specified value display field 4: Syst. OK

If the specifications are obtained:
- Press -> button.
- Press buttons -O- and -6- for function "End output" and confirm entry with -Q- button.
- Switch ignition off.

If the specifications are not attained:
- Press buttons -0- and -8- for "Read Measuring Value Block" function and confirm entry with Q button.

Indicated on display
- Press buttons -0-, -7- and -0- for "Display group number 70" and confirm entry with -Q- button.

Indicated on display: (1 -4 = Display zones)
- Press button -4- for "Basic setting" function ("Tank venting valve diagnosis" will be initiated).

Note: The engine must not be loaded during this diagnosis because the diagnosis will be interrupted and will not be started again until the engine is revved-up.

Indicated on display: (1 -4 = Display zones)

When the diagnosis is initiated by the Engine Control Module, the display in display zone 4 jumps from "Test OFF" to "Test ON."
- Run engine at idling speed until specification "EVAP OK" is displayed in display zone 4.

Note: If the display jumps from "Test ON" to "Test OFF" during the test, rev up briefly and the test will be repeated.

1) TEV means EVAP canister purge regulator valve

If "EVAP n OK" appears in display zone 4:
- Initiate output diagnostic test mode and activate EVAP Canister Purge Regulator Valve -N80-:

- Read readiness code.
If DTC memory has been erased or Engine Control Module separated from permanent (battery) positive, readiness code must be generated again.
If the specification "EVAP OK" is obtained:
- Press -> button.
- Press buttons -0- and -6- for function "End output" and confirm entry with -Q- button.
- Switch ignition off.

Checking for leaks
If a small or large leak is detected during the check of the Evaporative Emission (EVAP) system, proceed as follows.
- Switch ignition off.
- Check whether sealing cap of fuel tank is completely closed or whether sealing ring is leaking, replace if necessary.
- Repeat functional check.

Is the malfunction still present:
- Fold rear seat bench forward.
- Remove cover under seat bench.
- Check whether locking ring for fuel delivery unit is tight. It can be found under luggage compartment floor trim. Replace seal if it is malfunctioning.
- Tighten locking ring with special tool 3217.
- Check supply and return pipes on fuel delivery unit for leaks.
- Repeat functional check.

Is the malfunction still present:
- Remove rear right wheel housing liner.
- Check connecting pipes and hoses between Leak Detection Pump and EVAP canister, Refer to Evaporative Emissions System, Testing and Inspection. Removing and installing parts of Evaporative Emission , Refer to Evaporative Emissions System, Service and Repair (EVAP) system. Replace if necessary.
- Check wires and wire connections between EVAP canister and tank flap unit or tank ventilation valve for proper seal.
- Repeat functional check.

Is the malfunction still present:
- Remove EVAP canister and check for cracks and leaks, replace if necessary.
- Repeat functional check.