Purge system with leak test function - GF47.30-P-3016AMG
MODEL 164, 251 with ENGINE 156.980
with CODE (494) USA version
up to Model Year 8
MODEL 209 with ENGINE 156.982 with CODE (494) USA version
MODEL 211, 219 with ENGINE 156.983 with CODE (494) USA version
MODEL 216, 221 with ENGINE 156.984
with CODE (494) USA version
up to Model Year 8
Shown on fuel tank model 164
The legislator requires that no fuel vapors reaches the open air.
The leaktightness test for the fuel evaporation control system must be undertaken in three stages (function chain):
- Checking for a gross leak (leak ≥3 mm)
- Checking for a fine leak (leak ≥1 mm)
- Checking for a very fine leak (leak ≥0.5 mm)
Test for major leaks
The activated charcoal filter shutoff valve is closed (no longer actuated) and the purge control valve opened (actuated). Intake manifold vacuum present in fuel tank. This vacuum is measured by the tank pressure sensor.
If there is no vacuum build-up in the fuel tank (approx. -6 mbar within approx. 12 seconds) there is a major leak (e.g. tank cap missing, hose line loose)
The test will be interrupted and the error gross leak registered.
If the ME-SFI [ME] control unit detects a system with a substantial major leak, the fuel reserve warning lamp (A1e4) in the instrument cluster (A1) blinks and the message "CHECK FILLER CAP" appears in the multifunction display (A1p13).
If no leak for the fault major leak is found (there is a clear hissing noise if there is a leak of more than 3 mm), replace fuel tank pressure sensor. The fuel tank pressure sensor may have a fault which results in a signal which is constant but still plausible (sensor sticking).
Test for a minor leak
The fuel tank is replaced with the intake manifold vacuum applied. The purge control valve is closed at a vacuum of around -6 mbar. The system is closed and thereby airproof. Finally the vacuum is 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 minor leak. The test will be interrupted and the error fine leak registered.
Check for micro leakage
If no minor leak has been detected, the purge system is briefly enabled and a vacuum of approx. -6 mbar is built up again. The vacuum must not drop any faster than 0.1 to 0.15 mbar per second for a closed system (depending on the level of fuel in the tank).
If the vacuum drops more rapidly, the fault "micro leak" is registered.
The test for minor and micro leaks is aborted if an excessive lean correction of the lambda control takes place during the build-up of the vacuum.
The reduction in vacuum depends on the fuel level in the fuel tank and on degassing of the fuel. The degassing of the fuel is measured for a short time prior to the test by the fuel tank pressure sensor and is allowed for in the fault statement.
The activated charcoal canister shut-off valve is reopened (actuated) after the tests have been conducted.
Test requirements
- Engine at idle
- Vehicle stationary
- Drive position "D" or "R" is engaged
- Blocking time after engine start elapsed (approx. 16 minutes) or mixture adaptation occurring
- Lambda control enabled
- Intake air temperature < 45°C
- Coolant temperature for engine start < 100°C
- Air injection not active
- Air pressure > 780 hPa (which means that no test takes place above a height of about 2500 meters)
- Low loading of activated charcoal canister
- Fuel level in the fuel tank between approximately 1/4 and 3/4
- No fault in the activated charcoal canister shutoff valve
- No fault in the fuel tank pressure sensor
- No fault in the purge control valve
- Battery voltage > 11 V
The function of the purge control valve is checked at the same time by the activation. If the closed switchover valve jams, the major leak fault is stored.
In case of an implausible fuel level resulting from a defective fuel level sensor, the tests are not stopped.
| Component description for the ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000AMG | |
| Component description for the fuel tank | 75 | Model 164, 251 | GF47.10-P-2000AMG |
| 75 | Model 209 | GF47.10-P-2000AQ | |
| 75 | Model 211, 219 | GF47.10-P-2000AT | |
| 75 | Model 216, 221 | GF47.10-P-2000AX | |
| Component description for the activated charcoal canister | 77 | GF47.30-P-2010AMG | |
| Component description for the purge control valve | Y58/1 | GF47.30-P-2020AMG | |
| Component description for the fuel tank pressure sensor | B4/3 | GF47.30-P-2100AMG | |
| Component description for the activated charcoal filter shutoff valve | Y58/4 | GF47.31-P-2100AMG |