Purging System With Leak Test Function - GF47.30-P-3016MNF
Engine 176.9 in model 463
as of model year 2016 up to model year 2019
with code ZU8 (National version for USA)
Schematic diagram
Purge system function requirements with leak test, general
- Engine at idle
- Vehicle stationary
- Gear range "D" or "R"
- Blocking time after engine start elapsed (approx. 3 minutes) or self-adjustment of the mixture formation occurs
- Lambda control released
- Intake air temperature < 72°C
- Coolant temperature when engine started < 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 the fuel tank at least 30%
Purge system with leak test, function sequence
The function sequence for the purging system with leak test includes the following partial functions:
- 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 left and right purging switchover valve opens. The vacuum in the intake manifold reaches the fuel tank. The ME-SFI [ME] control unit directly actuates the activated charcoal canister shutoff valve and the left and right purging switchover valves.
Vacuum then builds up in the fuel tank, and is measured by the fuel tank pressure sensor.
The fully integrated transmission control unit (Y3/8n4) transmits the status of the gear range via drive CAN (CAN C) to the ME-SFI [ME] control unit (N3/10).
The ME-SFI [ME] control unit directly reads in the signals of the left lambda senor sensor element upstream of catalytic converter (G3/3b1), the right lambda senor sensor element upstream of catalytic converter (G3/4b1), the left lambda senor sensor element downstream of catalytic converter (G3/5b1), the right lambda senor sensor element downstream of catalytic converter (G3/6b1), the left charge air temperature sensor (B17/14), the right charge air temperature sensor (B17/15) and the coolant temperature sensor (B11/4). Purge system with leak test, general
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.)
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 detects a system with a gross leak, the fuel reserve warning lamp (A1e4) in the instrument cluster (A1) flashes and the message "CHECK FILLER CAP" appears in the multifunction display (A1p13). The message in the multifunction display is only emitted of a refueling > 25 l is recognized otherwise only the fault "gross leak" is stored in the ME-SFI [ME] control unit fault memory. The ME-SFI [ME] control unit transmits the request via drive CAN, powertrain control unit (N127), suspension CAN 1 (CAN E1), electronic ignition lock control unit (N73) and via interior CAN (CAN B) to the instrument cluster. The instrument cluster actuates the fuel reserve warning lamp.
While checking for fine leaks, a vacuum of about -6 mbar is built up again and the system is made airproof. The vacuum is then evaluated 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.
Function sequence for gross leak-very fine leak check
If no "fine leak" has been detected, purging is briefly enabled and a vacuum of approximately -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. The FSCU (N118) reads in the signals from the fill level sensor for the fuel tank fuel level indicator (B4) directly and sends them via the drive CAN to the ME-SFI [ME] control unit. Fuel outgassing is measured shortly before fuel tank pressure sensor is checked, and taken into account for fault indication. The ME-SFI [ME] control unit directly reads in the signals from the fuel tank pressure sensor.
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 left and right purging switchover valve is checked at the same time by means of actuation. If the closed switchover valves jam, the "Gross leak" fault is stored.
If there are faults recognized, then these are stored by the ME-SFI [ME] control unit in the fault memory and the engine diagnosis indicator lamp (A1e58) lights up in the instrument cluster. The ME-SFI [ME] control unit sends the request via interior CAN, electronic ignition lock control unit, suspension CAN 1, powertrain control unit and drive CAN to the instrument cluster. The instrument cluster actuates the engine diagnosis indicator lamp directly.
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