Purge System With Leak Test, Function - GF47.30-P-3017MRT
Engine 256.9 In Model 213, 238, 257, 290
up to model year 2021
with code 494 (US version)
Engine 256.9 In Model 222
with code 494 (US version)
Function requirements, general
- 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
The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10).
The front SAM control unit (N10/6) transmits the outside temperature via the interior CAN (CAN B), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and drive CAN to the ME-SFI [ME] control unit.
The fuel level in the fuel tank is detected by the left fuel tank fuel level indicator fill level sensor (B4/1) and the right fuel tank fuel level indicator fill level sensor (B4/2). The fuel system control unit (N118) reads in the signals of the fuel tank fill level sensors and transmits the information on the fill level via the drive CAN to the ME-SFI [ME] control unit.
When the fuel filler flap is open, the rear SAM control unit (N10/8) transmits the status via the interior CAN, the electronic ignition lock control unit, the suspension FlexRay, the powertrain control unit, and the drive CAN to the ME-SFI [ME] control unit.
Purge system with leak test, general
The leak test of the purge system takes place in two stages (function chain) and must detect the following leaks:
- Leak diam. ≥ 1 mm
- Leak diam. ≥ 0.5 mm
The leak tightness of the fuel tank is checked by the ME-SFI [ME] control unit by comparing the power consumptions during the generation of an overpressure in the fuel tank without reference leak 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 ME-SFI [ME] control unit directly actuates the fuel tank diagnostic module heating element.
The purging switchover valve (Y58/1) must be closed when doing this (switchover valve not actuated = purging inhibited). The ME-SFI [ME] control unit directly actuates the purge control valve.
Leak test
The leak test is performed according to the following procedure:
- The vehicle is parked and the ignition is switched off.
- The ME-SFI [ME] 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 fuel tank diagnostic module solenoid valve switches over and the fuel tank diagnostic module pump generates a reference pressure in the fuel tank. During this operation, the current is also measured.
If the current strength value for the reference leak is exceeded during measurement, the fuel tank and its aeration and ventilation system are tight. Otherwise, a leak is determined. The magnitude of the leak is recognized by the time the pump has to operate before a defined reference current is reached.
The diagnosis is canceled if the fuel filler cap (e. g. for refueling) is opened.
Any leaks detected, are stored in the fault memory of the ME-SFI control unit. Once a fault occurs for the second time, the engine diagnosis indicator lamp in the instrument cluster lights up (A1). The ME-SFI [ME] control unit transmits the engine diagnosis indicator lamp actuation request via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and user interface CAN (CAN HMI) to the instrument cluster.
The pressure buildup also depends on the fuel level in fuel tank.
Schematic diagram of purge system
| Electrical function schematic for purge system with leak test | Engine 256.9 in model 213, 238 up to model year 2021 with code 494 (US version) | PE47.30-P-2053-97DBA | |
| Engine 256.9 in model 222 with code 494 (US version) | PE47.30-P-2053-97SEM | ||
| Engine 256.9 in model 257, 290 up to model year 2021 with code 494 (US version) | PE47.30-P-2053-97XBB | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRT |