Checking Fuel Tank & Tank Venting System For Leaks With Tank Leakage Diagnosis Module (DM-TL) - 5-Series (E39) 6-Cylinder
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- If a leak in the tank ventilation system is indicated by CHECK ENGINE indicator lamp in the instrument cluster, a leak test must be carried out. First, fault memory of DME control unit must be read out and diagnosis conducted. If sensors are okay, then begin leak test. Following conditions must be observed to obtain plausible measuring results:
- Ensure contents of fuel tank are 25-75 percent.
- Park vehicle in workshop at least 2 hours before test so fuel temperature is about that of workshop temperature. Ideal fuel temperature is 50-68°F (10-20°C).
- Never refuel the vehicle directly prior to leak test due to strong gas emission by fresh fuel.
- To conduct leak test, remove luggage compartment mat and spare tire. Remove battery cover. Remove hexagon nut and plastic nut. See Fig 1. Remove cover of activated carbon canister upward.
- Disconnect electrical connector of activated carbon canister non return valve. See Fig 2. Connect Special Tool (12 6 410/411) to activated carbon canister non return valve and vehicle battery. See Fig 3. Activated carbon canister non return valve is closed by applying 12 volts. Ensure voltage is sufficient and do not reverse terminals. Remove tank filler cap and connect special tool (16 1 150) to tank filler neck. See Figure.
- Screw in rear towing eye and hook Special Tool (16 1 150) into it. Connect special tool to compressed air system of 116-145 psi (8-10 bar) with compressed air hose. See Figure. Connect pressure sensor with measuring range of 0-51 psi (0-3.5 bar).WARNING: Ensure pressure regulator on Special Tool (16 1 150) is set completely in "-" direction and non return cock between the pressure regulator and pressure sensor is closed.
- Select MEASURING TECHNOLOGY function on Diagnosis Information System (DIS). Set measuring range in accordance with pressure sensor to 0-51 psi (0-3.5 bar). Open non return cock on Special Tool (16 1 150) and increase pressure in tank system by.72 psi (.050 bar) with pressure regulator.WARNING: Do not increase pressure by more than 1.45 psi (.10 bar), as damage to fuel tank and tank ventilation system is possible.
- Close non return cock. Wait for about 20 seconds for system to settle. Read off pressure value, then wait 60 seconds. Read off final pressure value and compare with starting pressure value. If pressure drop is in area between.116-1.7 psi (.008-.012 bar), measurement must be repeated to obtain a confirming measurement. If pressure drop in 60 seconds is greater than.145 psi (.010 bar), system is leaking.
- Leak test can be carried out with a leak detector. Possible causes may be fuel filler cap, tank ventilation line (fuel tank-activated carbon canister-tank ventilation valve), tank ventilation valve (engine compartment), tank sensor on fuel tank or activated carbon canister non return valve (spare tire recess).