(Purging System With Leak Test Function - GF47.30-P-3016A)
Engine 177.9 in model 205
up to model year 2016
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 combustion engine and fed to the combustion process. The lawmaker also requires that the fuel tank is checked at the same intervals for leaktightness.
Schematic illustration of fuel tank
Function requirements, general
- Engine at idle
- Vehicle stationary
- Gear range "D" or "R" is engaged
- Blocking time after engine start elapsed (approx. 3 minutes) or self-adjustment of the mixture formation has taken place
- Lambda control released
- Charge air temperature less than 72°C
- Coolant temperature at engine start less than 100°C
- Air pressure above 780 hPa (in other words, no test at altitudes above approx. 2500 m)
- Low loading of activated charcoal canister
- Fuel level in fuel tank at least 15 %
- Battery voltage above 11 V
The ME-SFI [ME] control unit (N3/10) detects that the engine is running by interpreting the signals from the crankshaft Hall sensor (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.
The instrument cluster (A1) sends the vehicle speed via the user interface CAN (CAN HMI), electronic ignition lock control unit (N73), suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1) to the ME-SFI [ME] control unit.
The fully integrated transmission control unit (Y3/8n4) sends information on the gear range engaged via the drive train CAN to the ME-SFI [ME] control unit.
The charge air temperature is sensed by the left charge air temperature sensor (B17/14) and the right charge air temperature sensor (B17/15) The ME-SFI [ME] control unit directly reads in the signals from the charge air temperature sensors.
The coolant temperature is recorded by the coolant temperature sensor (B11/4). The ME-SFI [ME] control unit reads in the signals of the coolant temperature sensor directly.
The atmospheric pressure is sensed by the pressure sensor in the ME-SFI [ME] control unit. The ME-SFI [ME] control unit directly reads in the signals from the pressure sensor.
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 (N10/6) assesses the load on the on-board electrical system and sends this information 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.
Leak test
The leak test of the purge system takes place in three stages (function chain) and must detect the following leaks:
- Gross leak (leak equal to or greater than 2.5 mm)
- Fine leak (leak equal to or greater than 1 mm)
- Very fine leak (leak equal to or greater than 0.5 mm)
Test for gross leak/fine leak
To check for a gross leak, the activated charcoal canister shutoff valve closes and the purging switchover valves open. The vacuum from the engines reaches the fuel tank. Vacuum then builds up in the fuel tank, and is measured by the fuel tank pressure sensor. The ME-SFI [ME] control unit directly actuates the activated charcoal canister shutoff valve and the purge switchover valves.
If no vacuum build-up in the fuel tank is recorded (approx. -6 hPa within approx. 12 s), a major leak is present (e.g. tank cap open, hose line loose). The test will be interrupted and the "Gross leak" fault stored in the fault memory. If the ME-SFI [ME] control unit detects a system with a gross leak, its sends the request to actuate the fuel reserve warning lamp via the drive CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and user interface CAN to the instrument cluster. The instrument cluster implements the request accordingly. The additional message "CHECK FILLER CAP" is displayed on the instrument cluster if fueling of more than 20 l is detected. Otherwise, only the "Gross leak" fault is stored in the fault memory. While checking for fine leaks, a vacuum of about -6 hPa is built up again and the system is made airproof. The vacuum is then measured for approx. 30 s. The vacuum decay rate must not be greater than 0.3 to 0.5 hPa/s (depending on fuel level). If the vacuum drops more rapidly, there is a fine leak. The test is interrupted and the "Fine leak" fault is stored in the fault memory.
The pressure buildup depends on the fuel level in the fuel tank.
Checking for gross leak/very fine leak
If no "Fine leak" is detected, the ME-SFI [ME] control unit briefly enables purging. A vacuum of approx. -17 hPa is built up in the fuel tank again afterwards. With a closed system, the vacuum must not be reduced faster than 0.10 to 0.15 hPa/s (depending on the fuel level). If the vacuum is reduced faster, the "Very fine leak" fault is stored. The reduction in vacuum depends on the fuel level in the fuel tank and on fuel outgassing. Fuel outgassing is measured shortly before fuel tank pressure sensor is checked, and taken into account for fault indication. The activated charcoal canister shutoff valve is reopened after the tests. The test for fine and very fine leaks is aborted if an excessive lean correction of the lambda control takes place during the buildup of the vacuum. The function of the purge switchover valves is checked at the same time. If the closed purging switchover valves jam, the "Gross leak" fault is stored. In the event of detected faults, a fault message is shown in the instrument cluster. The ME-SFI [ME] control unit transmits the request for output of the message via the drive train CAN, the powertrain control unit, the chassis FlexRay, the electronic ignition lock control unit and the user interface CAN to the instrument cluster.
| Electrical function schematic for purge system with leak test | PE47.30-P-2052-97FBD | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-P-9998MNA |