Tank ventilation MSS65

The fuel vapors drawn out of the activated carbon filters are fed via the tank-ventilation valves to the engine for combustion, as controlled by the DME. The tank-ventilation valves feed the fuel vapors to the two idle actuators. The fuel vapors are only drawn off in part-load operation.

The occurrence of fuel vapors from the fuel tank system is heavily dependent on:

- the fuel and ambient temperatures

- air pressure

- the tank fill level

When de-energized, the tank-ventilation valves are closed. This means that with the engine at a standstill no fuel vapors from the activated carbon filter enter the collector intake pipe.

System test for tank ventilation

The system test for tank ventilation corresponds to the function test that also runs in the normal driving mode. Deviating from this, the minimum engine run time of approx. 5 minutes does not have to elapse for the system test. A lower oil temperature threshold is also applied.

Run conditions:

• Vehicle stationary
  
• Engine at operating temperature
  
• Engine at idle speed
  
• Air mass < 36 kg/h
  
• No other system tests or component activations active
  
• No steering angle changes
  
• Voltage fluctuations < 0.8 V
  
• Engine oil temperature > 50 °C
  
• No catalytic converter heating active
  
• No generator or air-conditioning compressor load changes
  
• No state change of the brake system