Purging System With Leak Test Function - GF47.30-P-3016MRA
Engine 274.9 in model 205 (except 205.047/053/054/147/247/253) with code 494 (US version)
Engine 274.9 in model 253 (except 253.354/954) with code 494 (US version)
Schematic diagram
Function requirements for system purging with leak test in general
- Engine at idle
- Vehicle stationary
- Gear range "D" or "R" (with automatic transmission)
- Blocking time after engine start elapsed (approx. 3 minutes) or self-adjustment of the mixture formation occurs
- Lambda control enabled, oxygen sensor, sensor element upstream of catalytic converter (G3/2b1)
- Intake air temperature via charge air temperature sensor upstream of throttle valve (B17/7) and charge air temperature sensor downstream of throttle valve (B17/9) < 72°C
- Coolant temperature over coolant temperature sensor (B11/4) for engine start < 100°C
- Air pressure >780 hPa (which means that no test takes place above an altitude of about 2500 meters)
- Low loading of activated charcoal canister
- Fuel level in fuel tank at least 30%, signal from fuel tank fuel level indicator fill level sensor, left (B4/1) (for code 916 (Fuel tank 66 l)) and fuel tank fuel level indicator fill level sensor, right (B4/2) via FSCU (N118) and drive train CAN (CAN C1)
- No fault in the activated charcoal canister shutoff valve
- No error on the left fuel tank fuel level indicator fill level sensor (for code 916 (Fuel tank with 66 l) and the right fuel tank fuel level indicator fill level sensor
- No fault in the purging switchover valve
- Battery voltage > 11 V
Purging system with leak test, general points
The legislator requires that no fuel vapors reaches the open air.
The leak test for the evaporative emission control system must take place in three stages (function chain) and recognizes the following leak:
- Gross leak (a leak the same or greater than a 2.5 mm dia.)
- Fine leak (a leak the same or greater than a 1 mm dia.)
- Very fine leak (a leak the same or greater than a 0.5 mm dia.)
Function sequence for purging system with leak test
The function sequence is subdivided into the following steps:
- Function sequence for gross leak-fine leak check
- Function sequence for gross leak-very fine leak check
Function sequence for gross leak-fine leak check
To check for a gross leak the activated charcoal canister shutoff valve closes and the purging switchover valve opens. The vacuum from the charge air pipe finds its way to the fuel tank.
Vacuum then builds up in the fuel tank, and is measured by the fuel tank pressure sensor.
If no vacuum builds up in the fuel tank (approx.-6 mbar within approx. 12 s) there is a major leak (e.g. tank cap open, hose line loose). The test will be interrupted and the error "gross leak" stored in the fault memory.
If the ME-SFI [ME] control unit (N3/10) detects a gross leak in the system, the fuel reserve warning lamp is actuated in the instrument cluster (A1) via the drive train CAN (CAN), the powertrain control unit (N127), the suspension FlexRay (Flex E), the electronic ignition lock control unit (N73) and the user interface CAN (CAN HMI).
The additional message "CHECK FILLER CAP" is issued in the IC if a fueling of >25 l is recognized. Otherwise only the error "gross leak" is saved in the fault memory.
While checking for fine leaks, a vacuum of about -6 mbar is built up again and the system is made airproof. The vacuum is them measured for approx. 30 seconds. The vacuum must not reduce more rapidly than 0.3 to 0.5 mbar per second (depends on fuel level). If the vacuum drops more rapidly, there is a fine leak.
The test will be interrupted and the error "fine leak" is stored.
If no leak can be found, although a "gross leak" fault is indicated (if the leak diameter is more than 2.5 mm, there should be a loud hiss), replace the fuel tank pressure sensor.
Function sequence for gross leak-very fine leak check
If no "fine leak" has been detected, purging is briefly enabled and a vacuum of about -6 mbar is then built up again. In a closed system, the vacuum must not drop faster than 0.10 to 0.15 mbar per second (depending on fuel level). If the vacuum dissipates more rapidly, 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 purging switchover valve is checked at the same time by the activation. If the closed switchover valve jams, the "gross leak" fault is stored.
If faults are detected, these are stored in the fault memory by the ME-SFI [ME] control unit and the symbol is actuated in the IC via the drive train CAN, powertrain control unit, suspension FlexRay, electronic ignition lock control unit and the user interface CAN.
| Electrical function schematic for system purging with leak test | PE47.30-P-2051-97FBA | ||
| Overview of system components for gasoline injection and ignition system with direct injection | Engine 274.9 in model 205 (except 205.047/053/054/147/247/253), 253 (except 253.354/954) with code 494 (US version) |
GF07.70-P-9998MRA |