2003 3BMXV04.4LEV

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General Description - Evaporative system monitoring permits detection of leaks in evaporative system with a diameter of .019" (.5 mm) and larger. By means of a Diagnostic Module-Tank Leakage (DM-TL), an electrical actuated pump located at atmospheric connection of evaporative canister, a pressure test of evaporative system is performed in following order:
- During reference leak measurement, electrical actuated pump delivers through reference restriction. Engine management system measures pump electrical current consumption. See Fig 1.
- During leak measurement, electrical actuated pump delivers through charcoal canister into fuel tank system. Pressure in evaporative system may be up to 25 hPa, depending on fuel level in tank. Engine management system measures pump electrical current consumption. A comparison of currents of reference leak measurement and leak measurement is a measure for leakage in tank. See Fig 2.
- After the test, remaining pressure in evaporative system is bled off through charcoal canister by switching off pump and solenoid. See Fig 3.
  
  Fig 1: Reference Leak Measurement
  Courtesy of BMW OF NORTH AMERICA, INC.
  
  Fig 2: Leak Measurement
  Courtesy of BMW OF NORTH AMERICA, INC.
  
  Fig 3: Bleeding Off Remaining Pressure
  Courtesy of BMW OF NORTH AMERICA, INC.
Monitoring Structure Of Leak Measurement - See Fig 4-Fig 6 .

Fig 4: Monitoring Structure Of Leak Measurement (1 Of 3)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 5: Monitoring Structure Of Leak Measurement (2 Of 3)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 6: Monitoring Structure Of Leak Measurement (3 Of 3)
Courtesy of BMW OF NORTH AMERICA, INC.
Diagnosis Frequency & MIL Illumination - See Fig 7-Fig 8 .

Fig 7: No Refueling Detected; Leak Greater Than .039" (1.0 mm)
Courtesy of BMW OF NORTH AMERICA, INC.

Fig 8: Refueling Detected; Leak Greater Than .019" (.5 mm)
Courtesy of BMW OF NORTH AMERICA, INC.
Evaporative Purge System Flow Check - Purge flow from charcoal canister through purge valve is monitored after fuel system adaptation is completed and the lambda controller is at closed loop condition. Diagnosis is started during regular purging.
Monitoring Cycle Of Evaporative Purge System Flow Check
- Step 1 - For Rich Or Lean Mixture
  Flow through purge valve is assumed as soon as lambda controller is compensating for a rich or a lean shift. After this procedure, diagnosis is completed and evaporative purge system resumes working normally.
- Step 2 - For A 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 the engine idle speed. A predetermined value is reached if the system functions properly and the diagnosis procedure is completed. To start the diagnosis function (step 2) several conditions have to be satisfied.
  - Vehicle speed = Zero.
  - Engine at idle speed.
  - Closed loop of lambda controller.
  - Coolant temperature greater than fixed limit.
  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. Engine idle speed variation should be less than fixed limit.
  - Step 3
    In case of a high load in idle, a variation of engine idle speed cannot be measured correctly in step 2. Therefore, purge valve will be opened after EVAP leak detection has finished. When valve opens, pressure and also pump current will drop. If pump current is greater than threshold, purge valve is operational. See Fig 9.
    
    Fig 9: Evaporative Purge System Monitoring Structure (Test Group 2BMXV04.4LEV)
    Courtesy of BMW OF NORTH AMERICA, INC.