Purging System With Leak Test Function - GF47.30-P-3016MRS
Engine 264.9 in model 205
with code 494 (US version)
Purge system with leak test, general
As per the legal requirements no fuel vapors should escape into the environment. For this reason, they are initially stored in the fuel tank (75) and then in the activated charcoal canister (77). If the activated charcoal canister (77) is fully loaded, the fuel vapors are intaken by the combustion engine and supplied to the combustion. The legislator also demands that the fuel tank (75) be checked at regular intervals for leaks.
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. 2, 500 m)
- Fuel level in fuel tank (75) 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 chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit (N3/10).
The ambient temperature is recorded by the outside temperature sensor (B14). The front SAM control unit (N10/6) reads in the signals of the outside temperature sensor directly, calculates the outside temperature, and transmits it 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 atmospheric pressure is recorded by the pressure sensor in the ME-SFI [ME] control unit The ME-SFI [ME] control unit reads in the signals of the pressure sensor directly.
The fuel system control unit (N118) transmits information about the fuel level via the drive train CAN to the ME-SFI [ME] control unit.
The front SAM control unit assesses the capacity utilization of the onboard electrical system and transmits the corresponding information to the ME-SFI [ME] control unit via the interior CAN, electronic ignition lock control unit suspension FlexRay, powertrain control unit and drive CAN.
A closed fuel filler cap is detected via the pressure monitoring of the fuel tank (75).
Purge system with leak test
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
- Leak equal to or greater than 0.5 mm
The ME-SFI [ME] control unit checks the leak tightness of the fuel tank (75) by comparing the power consumptions during the generation of an overpressure in the fuel tank (75) 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 purge control valve (Y58/1) must be closed in this connection (switchover valve not actuated, purging blocked).
Test sequence
- The vehicle parked and ignition switched off.
- The ME-SFI [ME] control unit enables diagnosis.
- The fuel tank diagnostic module solenoid valve (A101y1) closes the aeration and ventilation of the activated charcoal canister (77).
- The fuel tank diagnostic module pump (A101m1) pumps air through an internal reference leak. The fuel tank diagnostic module measures the current strength that is required for this 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 (75). During this operation the current is also measured.
If the amperage value for the reference leak is exceeded during the measurement, the fuel tank (75) and its aeration and ventilation system are leaktight; a leak is otherwise detected. The size of the leak is determined by the time the pump requires to achieve a defined reference current.
The pressure buildup also depends on the fuel level in the fuel tank (75). If the fuel filler cap is opened (e.g. for fueling), the diagnosis is canceled.
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 (A1) lights up. The ME SFI [ME] control unit transmits the request to actuate the engine diagnosis display 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 instrument cluster implements this request accordingly.
Schematic diagram of purge system
| Electrical function schematic for system purging with leak test | PE47.30-P-2051-97FBI | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MRS |