Evaporative Emissions System: Testing and Inspection
Evaporative Emissions System, Checking For Leaks
Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
- V.A.G 1551 scan tool
NOTE: The vehicle system tester V.A.G 1552 can be used instead of the VAG 1551 scan tool, however a print-out is not possible.
- V.A.G 1551/3 Cable
Test conditions
- Fuse No. 43 must be OK.
- No fault stored in DTC memory
- All electrical consumers, e.g. lights and rear window heating must be switched off
- If the vehicle is equipped with an air conditioner, this must be switched off.
- Throttle valve angle less than 10° % display group 03, display zone 3
- Coolant temperature less than 80 °C See display group 04, display zone 3
- Intake air temperature less than 60 °C See display group 04, display zone 4
Functional check
- Connect VAG 1551 scan tool ((V.A.G 1552). Start engine and select the engine control module with the "Address word" 01. Connecting scan tool and selecting engine control module:
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.
Indicated on display:
Read measured value block
Input display group number XXX
- Press keys 0, 7 and 1 for "Display group number 71" and confirm entry with Q key.
Indicated on display
Read measured value block 71 ->
Reed open Test OFF
- Press key 4 for the "Introduction of basic setting" function.
Indicated on display
System in basic setting 71 ->
Reed open Test ON
Indicated on display
System in basic setting 71 ->
Reed closed Test ON
The test of the evaporative emissions system will be initiated. First of all the function of the Reed contact (in the diagnosis pump - V144) will be checked by the control module.
Indicated on display
System in basic setting 71 ->
Reed closed Syst. Test Test ON
After approx. 10 seconds the diagnosis pump (V144) will be activated and build-up pressure in the fuel system.
Indicated on display
System in basic setting 71 ->
Reed open Syst. Test Test ON
The test will be initiated after approx. 50 seconds (when there is not sufficient pressure available in the fuel system can last up to 120 seconds).
Indicated on display
System in basic setting 71 ->
Reed open Check Test ON
The diagnosis pump (V144) switches off and the control module measures the time until the Reed contact closes.
Indicated on display
System in basic setting 71 ->
Reed closed Check.END Syst. OK
- Check the display in display zones 3 and 4: specified value display field 3: Meas.END, Specified value display field 4: Syst. OK
If the specifications are not attained:
- Checking for proper seal
If the specifications are obtained:
- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
- Switch off ignition.
Checking for leaks
If a small or large leak is detected during the check of the evaporative emissions system, proceed as follows.
- Switch off ignition.
- Check whether the sealing cap of the fuel tank is completely closed or the seal is leaking, replace if necessary.
- Repeat the functional check.
Is the fault still present:
- Fold rear seat bench forwards.
- Remove cover below seat bench.
- Check locking ring for fuel pump for tightness or if the seal is faulty and replace if necessary. Tighten locking ring using 3217 special tool. Check supply and return lines of at fuel pump for proper seal.
- Repeat the functional check.
Is the fault still present:
- Remove rear right wheel housing liner:
- Check pressure hose between diagnostic pump and EVAP canister for proper seal, item. 8 ; replace if necessary.
- Check wires and wire connections between EVAP canister and tank flap unit or tank ventilation valve for proper seal. Refer to "Evaporative Emissions System, Overview", Diagrams
- Repeat the functional check.
Is the fault still present:
- Remove EVAP canister and check for tears and leaks, replace if necessary.
- Repeat the functional check.