Purge system with leak test function - GF47.30-P-3016V

MODEL 203 with ENGINE 272.920 with CODE (494) USA version 

MODEL 211 with ENGINE 272.922 with CODE (494) USA version 

MODEL 203, 209 with ENGINE 272.940 with CODE (494) USA version 

MODEL 203 with ENGINE 272.941 with CODE (494) USA version 

MODEL 171 with ENGINE 272.942 with CODE (494) USA version 

MODEL 211 with ENGINE 272.943 with CODE (494) USA version 

MODEL 211 with ENGINE 272.944 with CODE (494) USA version 

MODEL 251 with ENGINE 272.945 with CODE (494) USA version 

MODEL 221 with ENGINE 272.946 with CODE (494) USA version 

MODEL 203, 209 with ENGINE 272.960 with CODE (494) USA version 

MODEL 171 with ENGINE 272.963 with CODE (494) USA version 

MODEL 211, 219 with ENGINE 272.964 with CODE (494) USA version 

MODEL 221 with ENGINE 272.965 with CODE (494) USA version 

MODEL 230 with ENGINE 272.966 with CODE (494) USA version 

MODEL 164, 251 with ENGINE 272.967 with CODE (494) USA version 

MODEL 203 with ENGINE 272.970 with CODE (494) USA version 

MODEL 211 with ENGINE 272.972 with CODE (494) USA version 

MODEL 221 with ENGINE 272.975 with CODE (494) USA version 

MODEL 221 with ENGINE 273.922 with CODE (494) USA version 

MODEL 164 with ENGINE 273.923 with CODE (494) USA version 

MODEL 221 with ENGINE 273.924 with CODE (494) USA version 

MODEL 164 with ENGINE 273.943 with CODE (494) USA version 

MODEL 211, 219 with ENGINE 273.960 with CODE (494) USA version 

MODEL 216, 221 with ENGINE 273.961 with CODE (494) USA version 

MODEL 211 with ENGINE 273.962 with CODE (494) USA version 

MODEL 164, 251 with ENGINE 273.963 with CODE (494) USA version 

MODEL 230 with ENGINE 273.965 with CODE (494) USA version 

MODEL 209 with ENGINE 273.967 with CODE (494) USA version 

MODEL 221 with ENGINE 273.968 with CODE (494) USA version 

Fig 1: Purge System Function Diagram - Shown On Engine 272 In Model 171 (With Leak Test)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The legislator requires that no fuel vapors reaches the open air. The leak-tightness test for the fuel evaporation control system must be undertaken in three stages (function chain):

• Check for a gross leak (leak ≥3 mm)
• Check for a fine leak (leak ≥1 mm)
• Check 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 indicator lamp in the instrument cluster blinks and the message "CHECK FILLER CAP" appears in the multifunction display (A1).

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.

The tests are not stopped if there is an implausible fuel level resulting from a defective fuel level sensor.