Fuel Tank Leak Diagnostic Module; General Information; Function - BMW N62 Series Service Training

New Generation N62 Engine

Fuel tank leak diagnostic module

- General information

A fuel tank leak diagnostic module is always fitted on US
vehicles to detect leaks in the tank and tank ventilation system.
The fuel tank diagnostic module is a run-on function which is
automatically started via the digital engine management system
when terminal 15 is switched off and if the assessment criteria
are fulfilled at the same time.
The fuel tank leak diagnostic module detects leaks measuring
over 0.5 mm in diameter anywhere in the entire tank system.
A leak is indicated by the MIL (malfunction indicator lamp).

- Function

The fuel tank leak diagnostic module generates excess pressure
of 20-30 mbar in the fuel tank using an electrically operated air
pump (vane pump). The pump flow required for this is calculated
by the digital engine management system and serves as the
indirect value for the tank pressure.
A comparison measurement is carried out by the fuel tank leak
diagnostic module before each measurement. To do this, excess
pressure is built up for 10-15 seconds using a previous leak of
0.5 mm as reference and the pump flow required for that
(20-30 mA) is measured.
If a lower pressure is detected in the subsequent pressure build-
up compared to the reference pump flow previously measured,
this signals a leak in the fuel system.
If the reference flow is exceeded, there is no leakage in the
system.
© BMW AG, Service Training
Course Contents/Background Material
Chapter 6 P.10