2003 3BMXV03.0UL2
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- Leak Measurement General Description -
Evaporative system monitoring permits detection of leaks in the evaporative system with a diameter of .019" (.5 mm) and greater. The Diagnostic Module-Tank Leakage (DM-TL), an electrically actuated pump located at the atmospheric connection of the evaporative canister, performs a pressure test of the evaporative system in the following order:
- During the Reference leak Measurement, the electrically actuated pump delivers air through the reference restriction. The engine-management system measures the pump's electrical current consumption in this phase. See Figure.
- During leak measurement, electrically actuated pump delivers air through charcoal canister to fuel-tank system. Pressure in evaporative system may be up to 25 hPa depending on the fuel level in the tank. The engine management system measures pump electrical current consumption. A comparison of the currents of the reference leak measurement and the leak measurement is an indication of the leakage in the tank. See Figure.
- After the test the remaining pressure in the evaporative system is bled off through the charcoal canister by switching off the 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 - Flow from charcoal canister through purge valve is monitored after fuel system adaptation is completed and lambda controller is at closed-loop condition. Diagnosis (evaporative purge system flow check) is started during regular purging.
- Monitoring Process Of Evaporative Purge System Flow Check -
Monitoring process of the evaporative purge system flow check includes following 3 steps:
- 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.
- For stoichiometric mixture or if first step fails, in this case lambda controller does not need to compensate for a deviation. Therefore, after finishing regular purging, purge valve is opened and closed abruptly several times. The effect of additional cylinder charge triggers a variation of engine idle speed. If a predetermined value is reached, diagnosis procedure is completed.
- For stoichiometric mixture or if threshold at second step is not reached, an additional procedure is performed. Purge valve is opened and idle air control valve simultaneously is closed to compensate idle speed increase. The effect is a decrease of the measured idle air mass by mass airflow sensor. If a predetermined value is reached, diagnosis procedure is completed. See Fig 1.