2003 3BMXV06.0N73

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Evaporative System Leak Measurement - Evaporative system monitoring permits detection of leaks in evaporative system with a diameter of .019" (.5 mm) and up. 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 the following order:
- During reference leak measurement, electrical actuated pump delivers through reference restriction. Engine-management system measures pump's electrical current consumption in this section. See Figure.
- During leak measurement, electrical actuated pump delivers through charcoal canister into fuel-tank system. Engine management system measures pump's electrical current consumption. A comparison of currents of reference leak measurement and leak measurement is a measure for leakage in tank. See Figure.
- After test, remaining pressure in evaporative system is bled off through charcoal canister by switching off pump and solenoid. See Figure.
Monitoring Structure Of Leak Measurement - See Figure-Figure .
Diagnosis Frequency & MIL Illumination - See Figure-Figure .
Evaporative Purge System Flow Check - Purge flow from charcoal canister through purge valve is monitored after fuel system adaptation is completed and lambda controller is at closed loop condition. Diagnosis is started during regular purging. See Fig 1.

Fig 1: Monitoring Structure Of Evaporative Purge System Flow Check
Courtesy of BMW OF NORTH AMERICA, INC.
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, 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 and increases the intake manifold pressure. If either the integral of idle speed variation or the integral of intake manifold pressure increase reach a predetermined value, the system functions properly and the diagnosis procedure is completed. To start the diagnosis function (step 2) several conditions have to be satisfied:
  1. Vehicle speed = 0.
  2. Engine at idle speed.
  3. Closed loop of lambda controller.
  4. Coolant temperature greater than fixed limit.
  5. Commanded engine idle speed variation less than a fixed limit.
  Furthermore, if the diagnosis has already been started and one of the conditions has not been satisfied continuously, the process will be interrupted and started again later.