Purge System With Leak Test, Function - GF47.30-P-3017MMY

ENGINE 157.9, 276.8, 278.9 in MODEL 166 (except 166.063) as of model year 2016 with CODE 494 (US version) 

ENGINE 157.9, 276.8, 278.9 in MODEL 292 with CODE 494 (US version) 

Function requirements for purge system with leak test 

• Engine switched off
• Circuit 15 OFF
• Ambient temperature between 4 and 35 °C
• Air pressure >780 hPa (which means that no test takes place above an altitude of about 2500 meters)
• Fuel level in fuel tank between 15 and 85 %
• Battery voltage > 11 V
• Tank cap closed
• No fault at involved actuators or sensors

  The leak test of the purge system takes place in two stages (function chain) and must detect the following leaks:

• Leak equal to or greater than 1 mm dia.
• Leak equal to or greater than Ø 0.5 mm

The leaktightness of the fuel tank is checked by the ME-SFI [ME] control unit (N3/10) by comparing the power consumption during generation of an overpressure in the fuel tank without and via the reference leak in the fuel tank diagnostic module (A101).

The purging switchover valve (Y58/1) must be closed when doing this (switchover valve not actuated = purging inhibited).

Test sequence:

• Vehicle parked and ignition switched off.
• ME-SFI control unit enables diagnosis.
• The shutoff valve in the fuel tank diagnostic module closes the aeration and venting of the activated charcoal canister.
• The pump in the diagnostic module pumps air through an internal reference leak and measures the current required for the procedure.
• The valve in the diagnostic module switches over and the pump pumps a reference pressure into the fuel tank. During this operation, the current is also measured.

If the value of the current for the reference leak is exceeded during measurement, the fuel tank and its aeration and ventilation system are leaktight, otherwise a leak is present. The magnitude of the leak is recognized by the time the pump has to operate before a defined reference current is reached.

If the tank cap (e.g. when fueling) is opened, the diagnosis is interrupted.

Any leaks detected, are stored in the fault memory of the ME-SFI control unit. An error message also appears in the instrument cluster.

The pressure buildup depends on the fuel level in the fuel tank. This is determined by the left and right fuel tank fuel level indicator fill level sensors (B4/1, B4/2) and used by the ME-SFI {ME] control unit during the evaluation.

Schematic diagram of purge system