Purge System With Leak Test, Function - GF47.30-P-3017MND
Engine 276.8 In Model 213, 238
up to model year 2021
with code 494 (US version)
Purge system with leak test, general
As per the legal requirements no fuel vapors should escape into the environment. Therefore they are first stored in the fuel tank and in an activated charcoal canister. If the activated charcoal canister is fully loaded, the fuel vapors are suctioned at regular intervals out of the internal combustion engine and led to the combustion.
The lawmaker also requires that the fuel tank is checked at the same intervals for leaktightness.
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 (i.e. no testing above an altitude of approx. 2500 m)
- 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 Ø 1 mm
- 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 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).
In order to avoid false measurements caused by condensation or ice formation, the channel that acts as a reference leak is heated by the fuel tank diagnostic module heating element (A101r1).
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 fuel tank diagnostic module solenoid valve (A101y1) closes the aeration and venting of the activated charcoal canister.
- The fuel tank diagnostic module pump (A101m1) pumps air through an internal reference leak and measures the current that is required for the procedure.
- The solenoid valve in the diagnostic module switches over and the pump generates a reference pressure in 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 [ME] control unit. After double occurrence of a fault, the engine diagnosis indicator lamp in the instrument cluster illuminates.
The pressure buildup also depends on the fuel level in 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
| Electrical function schematic for purge system with leak test | PE47.30-P-2053-97DBF | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MND |