Functional description

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The diagnosis module for tank leakage is located on the activated carbon filter.

The leak test of the tank-ventilation system takes place after the drive cycle after stopping the engine. Various processes run in the after-run time of the engine management system:

Fig 1: Identifying Fuel Tank Leakage Diagnosis Module

Courtesy of BMW OF NORTH AMERICA, INC.

Index	Explanation
1	Fuel tank leakage diagnosis module
2	4-pin plug-in connection
3	Connection for tank vent line
4	Dust filter
5	Activated carbon filter
6	Connection for scavenging air line

The tank-leak diagnosis carried out within the framework of OBD 2 is based on the overpressure method. The tank-leakage diagnosis indicates a leakage where the diameter is greater than 0.5 mm and 1 mm. During the course of diagnosis, the tank-ventilation valve closes the connection to the intake pipe. At the start of the diagnosis, the leakage diagnosis pump pumps via a defined leakage of 0.5 mm diameter. The necessary current consumption is stored as an internal reference value. This is followed by the actual tank-leak diagnosis. The leak diagnosis pump pumps air into the tank-ventilation system. The current used is continuously measured. The comparison between the currently used current and the stored reference current indicates the type of leak (minor leak, superfine leak).