Operation CHARM: Car repair manuals for everyone.
Home >> Audi >> 1997 >> A4 Sedan (8D2) L4-1.8L Turbo (AEB) >> Repair and Diagnosis >> Powertrain Management >> Emission Control Systems >> Evaporative Emissions System >> Testing and Inspection >> Fuel Tank Ventilation and the EVAP System

Fuel Tank Ventilation and the EVAP System

FUEL TANK VENTILATION AND EVAP SYSTEM, CHECKING

Test Conditions:
- Check DTC memory (scan tool function 02)
- All electrical consumers shut off-radiator coolant fan should not be running during the test
- A/C switched off
- Intake air temperature less 90°C (194°F)
- Read Measuring Value Block, display group 4 (004), display field 4
- Coolant temperature less than 95°C (194°F)
- Read Measuring Value Block, display group 4 (004), display field 3
- Throttle valve angle less than 10°.
- Read Measuring Value Block, display group 3 (003), display field 3

Functional Check:
- Let engine idle.
- Connect VAG1551 or VAG1552 scan tool and press -1- button to select "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.
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.
Indicated on display:

Read Measuring Value Block HELP
Input display group number XXX

- Press buttons -0-, -7- and -1- to input display group number 71 (071), and press -Q- button to confirm.
Indicated on display:

Read Measuring Value Block 71 ->
Reed cl. Test OFF

- Check condition in display field 1.
- Specified display: "Reed cl." (reed closed)

If "Reed op." (reed open) appears in display field 1:
- Open fuel tank filler cap briefly to reduce pressure in fuel reservoir and close reed contact.

If display is OK:
- Let engine idle.
- Press -4- button to select "Basic Setting" function 04.
Indicated on display:

System in Basic Setting 71 ->
Reed cl. Test OFF

- Check operation of reed contact from control module.
Indicated on display:

System in Basic Setting 71 ->
Reed op. Test OFF

The Leak Detection Pump (LDP) is activated, and creates pressure in the fuel tank system.
Indicated on display:

System in Basic Setting 71 ->
Reed op. Syst. Test Test ON

After approx. 30 sec. (with sufficient pressure in fuel system), the leakage test begins.
Indicated on display:

System in Basic Setting 71 ->
Reed op. Check Test ON

The leak detection pump shuts off, and the control module measures the time until the reed contact closes.
Indicated on display:

System in Basic Setting 71 ->
Reed cl. Check.END Syst. OK

- Stop engine and switch ignition off.
The leakage test has ended (system OK). or...
If the test sequence ends, and one of these other results is displayed:

System in Basic Setting 71->
Reed cl. Lg. leak Check.END Syst.n.OK

System in Basic Setting 71->
Reed cl. Sm.leak Check.END Syst.n.OK

Check tank ventilation system for leaks.

Checking For Leaks:
If a small or large leak has been detected by pressure testing via the leak detection pump:
- Stop engine and switch ignition off.
- Check that fuel filler cap is completely closed and properly sealed; replace seal if malfunctioning.
- Under luggage compartment trim, check that fuel pump module lock ring is tight and properly sealed.
- Replace seal if malfunctioning.
- Tighten lock ring with special tool 3217.
- Check fuel supply and return lines for leaks.
- Remove EVAP canister from spare tire well, check for cracks and leaks, and replace if necessary.
- Check for secure fit of hoses and clamps to lines between leak detection pump (left rear wheelhousing) and EVAP canister purge regulator valve -N80- in engine compartment.
- Start engine and let idle.
- Start diagnostic test sequence using VAG1551 scan tool.
Indicated on display:

System in Basic Setting 71 ->
Reed cl. Check.END Syst. OK

- Stop engine and switch ignition off.
The leakage test has ended (system OK). or...
If the test sequence ends, and one of the following results is indicated on the display:

System in Basic Setting 71->
Reed cl. Lg. leak Check.ENDSyst.n.OK

System in Basic Setting 71->
Reed cl. Sm.leak Check.END Syst.n.OK

- Check tank system for leaks.
- Start engine and let idle.
- Start diagnostic test sequence using VAG1551 scan tool.
Indicated on display:

System in Basic Setting 71 ->
Reed op. Syst. Test Test ON

The Leak Detection Pump (LDP) starts running.
Testing for a small or large leak with a non-flammable leak detector spray is possible only with the LDP running.

- With LDP running, check for leaks at following points using non-flammable, environmentally safe leak detector spray:
- Lines between LDP and EVAP canister
- EVAP system check for cracks and/or leaks on all connections, by removing EVAP canister from spare tire well on floor of vehicle luggage compartment.
- Lines between EVAP canister and EVAP canister purge regulator valve -N80- (from canister along vehicle floor toward engine compartment).
- Vent line between fuel pump module sealing flange (under luggage compartment trim) and fuel filler neck.
- Fuel pump module sealing flange and seal (under luggage compartment trim); if necessary, tighten using special tool 3217; check supply and return lines for leaks.





- When installing seal for flange, make sure that two arrows on tank and flange are aligned exactly.

Front-wheel-drive and quattro are installed differently, and there are two different alignment arrows on the sealing flange.
Indicated on display:

System in Basic Setting 71 ->
Reed cl. Check.END Syst. OK

The leakage test has ended.

NOTE: In order to complete a leakage test of the entire system, the diagnostic sequence must be repeated several times.
pro multis · About Operation CHARM