Test Group TBM5.4VJGFEK

Evaporative Purge System Monitoring General Description -  Purge flow from the charcoal canister through the purge valve is monitored after fuel system adaptation is completed and the lambda controller is at closed loop condition. See Figure. The diagnosis is started during regular purging. See Fig 1.

• Step 1 (For Rich Or Lean Mixture) -  Flow through the purge valve is assumed as soon as the lambda controller is compensating for a rich or a lean shift. After this procedure, diagnosis is completed and the evaporative purge system resumes working normally.
• Step 2 (For Stoichiometric Mixture) -  In this case the lambda controller does not need to compensate for a deviation. Therefore, after finishing the regular purging, the purge valve is opened and closed abruptly several times. The effect of additional cylinder charge triggers a variation of engine idle speed. A predetermined value is reached if the system functions properly and the diagnosis procedure is completed.

  To start the diagnosis function, several conditions have to be satisfied:

  • Vehicle speed = 0.
  • Engine at idle speed.
  • Closed loop of lambda controller.
  • Coolant temperature greater than 207°F (97°C).
  • Air conditioning system not active.
  • Transmission in gear position, not "P" or "N".
  Furthermore, if diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted and started again later.
  • No throttle position change.
  • Engine idle speed variation = 560 < n < 720 RPM.
  • Engine load variation = 1.3 < TL < 1.8 (ms).
  • Steering wheel rotary motion = < 5 degrees.
    Fig 1: Identifying Evaporative System

    Courtesy of BMW OF NORTH AMERICA, INC.