Evaporative Emissions System: Testing and Inspection
Evaporative (EVAP) emissions system
Leak diagnosis, functional description
The Evaporative emissions system (including fuel tank) is equipped with leak diagnosis capability which will detect if the system is leaking.
This diagnostic operates by pressurizing the system and is capable of sensing leakage in cases where the source is at least 1 mm in diameter.
During diagnosis, the fuel system diagnostic pump V144 builds up a pressure of approximately 30 bar in the EVAP system. The pump will switch OFF when correct pressure is obtained. If pressure falls below a certain value, the pump will switch ON again. The On Board Diagnostic monitors the time between the switched ON periods and if it is too short, will register a malfunction in the Diagnostic Trouble Code memory.
Note: Production hose connections are secured with either spring or clamp type clips.
When replacing an existing clip, always use the spring-type.
VAS 5024 or VAG 1921 pliers are recommended for installing spring clips.
Observe safety precautions
Observe Rules for cleanliness
Evaporative Emissions System, Checking
Special tools
- V.A.G 1551/1552 Scan Tool
NOTE: The V.A.G 1552 Scan Tool can be used instead of the V.A.G 1551; however, a print-out is not possible.
- V.A.G 1551/3 adapter cable
Checking requirements
- All fuses must be OK.
- No malfunctions stored in DTC memory:
- All electrical consumers switched OFF, e.g. lights and rear window heater must be OFF
- A/C switched OFF, if equipped.
- Throttle valve angle less than 10 % display group 03, display zone 3
- Engine Coolant Temperature less than 99 °C See display group 04, display zone 3
- Intake Air Temperature 95 °C maximum See display group 04, display zone 4
Function test
- Connect V.A.G 1551/1552 Scan Tool.
- Start engine and let idle.
- Press 0 and 1 buttons to select Address word 01 "Engine electronics".
Display will appear as shown
Rapid data transfer HELP
Select function XX
- Press 0 and 8 buttons to select Function 08: "Read measuring value block".
- Press Q button to enter input.
Display will appear as shown
Read measuring value block
Input display group number XXX
- Press 0, 7 and 1 buttons to select "Display group 71".
- Press Q button to enter input.
Display will appear as shown
Read measuring value block 71 ->
Reed closed Terminated Test OFF
or
Display will appear as shown
Read measuring value block 71 ->
Reed closed Check END System OK
- Check display in zone 1:
If "Reed open" appears in display group 1:
- Briefly open fuel tank cap to release pressure in fuel tank.
Reed switch will close
If specification obtained:
- Press 0 and 4 buttons to select Function 04 "Basic setting".
- Press Q button to enter input.
Display will appear as shown
System in basic setting 71 ->
Reed closed Test ON
- Evaporative emissions system test will begin. First, the Function of the Reed switch (in Leak Detection Pump -V144-) is checked by the ECM.
- After approx. 10 seconds the Leak Detection Pump -V144- will be activated and pressure will build-up in the system.
Display will appear as shown
System in basic setting 71 ->
Reed open System Test Test ON
- The test will be initiated after approx. 50 seconds, when sufficient pressure has built up in the fuel system; however, it could take as long as 120 seconds to build the pressure if the fuel level is low.
Display will appear as shown
System in basic setting 71 ->
Reed open Check Test ON
- The Leak Detection Pump -V144- switches OFF and the ECM measures the time until the Reed contact closes.
Display will appear as shown
System in basic setting 71 ->
Reed closed Check END System OK
- Check display in zones 3 and 4:
If specifications in display field 3 "END of Test" and display field 4 "System OK" are reached:
- Press -> button.
- Press 0 and 6 buttons to select Function 06: "End transfer".
Engine must not be under load during this diagnosis because diagnosis will be interrupted and will not restart until engine is accelerated.
Display will appear as shown (1 to 4 = Display zones)
System in basic setting 70 ->
1 2 3 4
- 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 idle until specification "TEV OK" is shown in display zone 4.
NOTE: If display changes from "Test ON" to "Test OFF" during test, briefly accelerate engine and test will repeat.
If "TEV not OK" appears in display zone 4:
- Perform Output Diagnostic Test Mode and activate the EVAP canister purge regulator valve N80:
- Display Readiness code:
- Readiness code must be reset if ECM is subject to low voltage with ignition ON or if DTC memory is erased.
If specification "TEV OK" obtained:
- Press -> button.
Display will appear as shown
Rapid data transfer HELP Select function XX
- Press 0 and 6 buttons to select Function 06: "End transfer".
- Press Q button to enter input.
- Switch ignition OFF.
Leak checking
If either a small or large leak is detected during the Evaporative emissions system leak check, proceed as follows:
- Check fuel tank cap is secure and seal is not damaged. Replace if necessary.
- Repeat functional check.
If malfunction still present:
- Fold rear seat bottom forward.
- Remove cover under seat bottom.
- Check if fuel delivery unit nut is tight and that seal is not damaged. Replace if necessary.
- Tighten lock ring with special 3217 tool.
- Repeat function test.
If malfunction still present:
- Remove right rear wheel housing liner:
- Check pressure hose between Leak Detection Pump (LDP) -V144- and EVAP canister (item 5 ). Replace if necessary.
- Check connecting lines and hoses between EVAP canister and EVAP canister purge regulator valve -N80-. Refer to "Evaporative Emissions System, Overview�, Diagrams
- Repeat function test.
If malfunction still present:
- Remove EVAP canister from wheel housing and check for cracks and leaks. Replace if necessary.
- Repeat functional check.