Purging System With Leak Test Function - GF47.30-P-3016KJ
ENGINE 281.910 in MODEL 453.3/4
with CODE 494 (US version)
Schematic diagram
Purge system function requirements with leak test, general
- Circuit 87 M (engine management ON)
- Engine at idle
- Vehicle stationary
- Gear range "D" or "R" engaged, via drive train CAN (CAN C) from DKG control unit (N15/13) (for code 429 (twinamic))
- Blocking time after engine start elapsed (approx. 3 minutes) or self adjustment of the mixture formation occurs
- Lambda control over oxygen sensor downstream of CAT (G3/1) and oxygen sensor upstream of CAT (G3/2) released
- Intake air temperature over intake air temperature sensor (B17) < 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 (75) at least 30%, signal from fuel tank fuel level indicator fill level sensor (M3/3b1) via IC (A1) (for code K35 (IC with monochrome display)) or (for code K36 (IC with color 8.9 cm (3.5") display)), via the interior CAN (CAN B) to ME-SFI [ME] control unit (N3/10)
- No fault in the activated charcoal canister shutoff valve
- No fault on fuel tank fuel level indicator fill level sensor
- No fault on fuel tank bleed valve
- Battery voltage > 11 V
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.)
Purge system with leak test, function sequence
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
For checking for a gross leak the activated charcoal canister shutoff valve closes and the fuel tank bleed valve opens. The suction vacuum reaches the fuel tank.
As a result, vacuum builds up in the fuel tank (75) and is measured by the fuel tank pressure sensor.
If no vacuum builds up in the fuel tank (75) (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 gross leak system, the multifunction display (A1p13) is actuated via the interior CAN and the IC (for code K35 (IC with monochrome display)) or (for code K36 (IC with color 8.9 cm (3.5") display)), (warning lamp flashes). The additional message "CHECK FILLER CAP" is output in the multifunction display, if a refueling volume of > 20 l is detected. 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 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 (75) 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 fuel tank bleed valve is checked at the same time through actuation. If the closed fuel tank bleed valve jams, the "gross leak" fault is stored.
For recognized faults, these are stored by the ME-SFI [ME] control unit in the fault memory and the engine diagnosis indicator lamp (A1e58) is actuated by the interior CAN, and the IC (for code K35 (IC with monochrome display)) or (for code K36 (IC with a colored 8.9 cm (3.5") display)) is actuated.
| Electrical function schematic for system purging with leak test | PE47.30-P-2051-97BBA | ||
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