Fuel Tank Pressure Sensor: Testing and Inspection
Checking Fuel Tank And Tank Ventilation System For Leaks
NOTE:
The following procedure is only applicable to vehicles without the tank leak diagnosis module.
Check tank venting system if a leak is suspected.
CAUTION!
Emerging fuel vapors!
Carry out all operations in well ventilated rooms only or use appropriate fume extraction units.
Observe country-specific accident prevention and occupational safety regulations.
Comply with the following conditions in order to obtain plausible test results:
- Content of fuel tank:
1. Max. 90% (approx. 65 l: equals a sensor resistance of approx. 680 Ohms.
2. Min. 15% (reserve indicator lamp "off").
- Park the car in the workshop at least 2 hours before the test so that the fuel temperature is approximately that of the workshop temperature (ideal fuel temperature approx. 10...20 °C).
- Never refuel the vehicle directly prior to the leak test due to the strong emission of gas by the fresh fuel.
Remove carbon canister underguard.
Unlock connection for vent line to dust filter (1) on carbon canister and detach.
Using special tool 16 1 157, seal opening for connection (1) on carbon canister.
Remove tank cap and connect special tool 16 1 174 to tank filler neck.
Using adjusting wheel (1), clamp special tool 16 1 174 firmly to tank filler neck.
CAUTION!
Set pressure regulator on special tool 16 1 171 fully in "-" direction.
Connect special tool 16 1 171 using compressed air line (1) to garage compressed air system (8...10 bar).
Connect pressure sensor (2) from Diagnosis and Information System with a measuring range of 0...3.5 bar.
CAUTION!
Do not connect fast-release coupling (3) of special tool 16 1 171 yet.
Select "Measurement" function on Diagnosis and Information System (DIS).
Adjust measuring range according to pressure sensor to 0-3.5 bar.
Using pressure regulator on special tool 16 1 171, increase pressure by 0.050 bar.
Connect special tool 16 1 174 to fast-release coupling of special tool 16 1 171.
Using pressure regulator on special tool 16 1 171, reset gauge pressure in fuel tank to 0.050 (+0.010) bar.
CAUTION!
Do not under any circumstance increase pressure by more than 0.100 bar as this would result in damage to the fuel tank and venting system.
Using special tool 13 3 010, disconnect supply line from special tool 16 1 171 to tank filler neck. Allow a rest period of approx. 20 secs.
Read off and note down starting pressure value.
Wait 60 secs.
Read off final pressure value and compare with starting pressure value.
Measurement evaluation:
Pressure drop between 0.003 and 0.004 bar. Measure again.
Pressure drop in 60 secs. >= 0.005 bar System leaking beyond permitted levels.
Carry out leak test.
Remove special tool 13 3 010 from supply line from special tool 16 1 171 to filler neck.
Using pressure regulator on special tool 16 1 171 set gauge pressure in fuel tank again to 0.050 (+0.010) bar.
Allow a rest period of approx. 20 secs.
Unlock special tool 16 1 157 and detach from carbon canister.
Allow measured value in display of Diagnosis and Information System to drop to ambient pressure.
Attach vent line to dust filter (1) to carbon canister.
Wait 60 secs.
Read off pressure value and compare with ambient pressure.
Measurement evaluation:
Pressure increase between 0.004 and Measure again.
0.006 bar.
Pressure increase in 60 secs. >= 0.007 bar Narrowing of cross-section in vent line from carbon canister to dust filter and/or in dust filter.
Carry out troubleshooting.
Remove rear right wheel arch trim.
Release screw (1) and remove dust filter (2).
Seal dust filter (2) with special tool 16 1 161.
Using pressure regulator on special tool 16 1 171 increase pressure in fuel tank by 0.050 (+0.010) bar.
Using special tool 13 3 010, disconnect supply line from special tool 16 1 171 to tank filler neck. Allow a rest period of approx. 20 secs.
Read off and note down starting pressure value.
Wait 60 secs.
Read off final pressure value and compare with starting pressure value.
Measurement evaluation:
Pressure drop between 0.026 and 0.039 bar. Measure again.
Pressure drop in 60 secs. >= 0.040 bar Vent line between carbon canister and dust filter and/or dust filter leaking to non-permitted levels.
Carry out leak test on above-mentioned components.