BMW X5: US National Version
Fuel tank leakage diagnosis module
The fuel system leak test is regularly conducted when the engine is switched
off. Here, the following processes
are executed during the DME run-down period:
- Initial situation
During normal engine operation, the switchover valve in the diagnosis module
is in the "Regeneration"
position. Fuel vapors are stored in the activated charcoal filter and fed
into the engine depending on the
actuation of the fuel evaporation control valve (refer to "Fuel tank
ventilation").
- Starting conditions check
After the engine is switched off, the conditions necessary to restart are
checked:
- Engine off
- Battery voltage between 11.5 and 14.5 volts
- No fault memory entry in the DME regarding diagnosis module for tank
leak or tank-ventilation
system
- Fuel level greater than 10 % and less than 90 %
If the result is positive, tank leakage diagnosis is started with a
comparison measurement.
- Comparison measurement
The fuel evaporation control valve is always closed when the engine is
switched off. The switchover
valve in the diagnosis module remains in the "Regeneration" position. The
electric leakage diagnosis
pump impels fresh air from the surrounding area through a defined leak of
0.5 mm diameter. The current
draw needed for this is stored as a value. The actual tank leakage diagnosis
then follows.
- Tank leakage diagnosis:
The fuel evaporation control valve remains closed. The switchover valve
in the diagnosis module is
switched to the "Diagnosis" position. The leakage diagnosis pump impels
fresh air from the surrounding
area into the tank, causing the interior pressure to slowly increase. At the
start of tank leakage diagnosis,
the interior pressure is equal to the ambient pressure. The current draw is
therefore low. As the pressure
inside the tank increases, the current draw also increases. The DME
evaluates the current draw of the
leakage diagnosis pump.
- Pump current evaluation
The DME evaluates the increase in the current draw over a certain time.
If the current draw exceeds the value stored within this time, the fuel
system is considered to be OK.
Tank leakage diagnosis is ended.
If the current draw does not reach the value stored, the fuel system is
considered to be defective.
Tank leakage diagnosis allows a difference to be made between:
- Major leak, e.g. fuel cap missing
- Minor leak
- Micro-leak
The relevant fault is entered in the DME fault memory. Tank leakage
diagnosis is then ended.
- End of tank leakage diagnosis:
The switchover valve is switched back to the "Regeneration" position. The
DME run-down period
remains available for other functions.
Tank leakage diagnosis can also be started with the BMW diagnosis system. In
this case, the processes run as
described above.
Subject to change.
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General information
Thescope of delivery of the BMW display key includes
an additional mechanical key. If the display
key is used, the mechanical key should be
carried with you, for instance in the wallet. The
mechanical key is used like the integrated key.
The display key supports all functions of