Purge system with leak test function - GF47.30-P-3016CY
MODEL 204.0/2 with ENGINE 272.947 with CODE (494) USA version up to Model Year 2008
MODEL 204.0 with ENGINE 272.948 with CODE (494) USA version up to Model Year 2008
MODEL 204.0/2 with ENGINE 272.961 with CODE (494) USA version up to Model Year 2008
MODEL 204.0 with ENGINE 272.971 with CODE (494) USA version up to Model Year 2008
The legislator requires that no fuel vapors reaches the open air. Leak testing of the fuel evaporation control system must take place in three stages (function chain) and must detect leaks with a diameter of over 0.5 mm:
- Test for major leaks (equal to or greater than 3 mm)
- Test for fine leaks (equal to or greater than 1 mm)
- Test for micro-leaks (equal to or greater than 0.5 mm)
Test for major leaks
The activated charcoal filter shutoff valve is closed and the purge control valve opened. Intake manifold vacuum present in fuel tank. This vacuum is measured by the fuel tank pressure sensor.
If there is no vacuum build-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" registered.
If the ME-SFI [ME] control unit (N3/10) 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).
Test for a minor leak
The purge control valve is closed at a vacuum of around -6 mbar. The system is closed and thereby 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 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 reduction in vacuum depends on the fuel level in the fuel tank and on degassing of the fuel. 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 filter shutoff valve is reopened after the tests.
Test requirements
- Engine at idle
- Vehicle stationary
- Drive position "D" or "R" engaged (for automatic transmission 722.9)
- Blocking time after engine start elapsed (approx. 16 minutes) or self adaptation of mixture formation 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 an altitude of about 2500 meters)
- low loading of activated charcoal filter
- Fuel level in the fuel tank between approximately 1/4 and 3/4
- No fault in the activated charcoal filter shutoff valve
- No fault on fuel level indicator sensor, left or right (B4/1, B4/2)
- No fault in the purge control valve
- Battery voltage > 11 V
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 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.
If no leakage for the fault "gross leak" is found (there is a clear hissing noise if a leak of more than 3 mm exists), replace fuel tank pressure sensor. The fuel tank pressure sensor can be so defective that the signal is constant but not plausible (pressure sensor stuck).
| Electrical function diagram for system regeneration with leak test | PE47.30-P-2051-99FAA | |||
| Component description for the ME-SFI [ME] control unit | N3/10 | GF07.61-P-6000CY | ||
| Component description for a fuel tank | 75 | GF47.10-P-2000CY | ||
| Component description for the activated charcoal filter | 77 | GF47.30-P-2011CY | ||
| Component description for the purge control valve | Y58/1 | GF47.30-P-2020CY | ||
| Component description for the fuel tank pressure sensor | B4/3 | With code 494 USA version |
GF47.30-P-2101CY | |
| Component description for the activated charcoal filter shutoff valve | Y58/4 | With code 494 USA version |
GF47.31-P-2101CY | |
| Component description for an engine diagnosis indicator lamp | A1e58 | GF54.30-P-5010CY | ||