Test Group YBMXTO4.4E53, YBMXTO4.453M & YBMXV04.9S62
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NOTE:
The evaporative system monitoring permits the detection of leaks in the evaporative emission control system with a diameter of 1 mm and up.
- Evaporative System Monitoring General Description -
By means of a Diagnostic Module Tank Leakage (DMTL) an electrically actuated pump located at the atmospheric connection of the charcoal canister, a pressure test of the evaporative system is performed in the following order:
- During the Reference leak Measurement, the electrically actuated pump delivers through the reference restriction. The engine management system measures the pump's electrical current consumption in this section. See Fig 1.
- During the Rough Leak Measurement, the electrical actuated pump delivers through the charcoal canister into the fuel-tank system. The pressure in the evaporative system may be up to .3625 psi (25 hPa) depending on the fuel level in the tank. The engine management system measures the pump's electrical current consumption. A comparison of the currents of the reference leak measurement and the rough leak measurement is a measure for the leakage in the tank. See Fig 2.
- During the pressure test the purge valve needs to be shut. After the test, canister purge is resumed and consequently the remaining pressure in the evaporative system is bled off. See Fig 3.
- Monitoring Structure Of Leak Measurement - For EVAP system monitoring structure of leak measurement, see Fig 4.
- Diagnosis Frequency & MIL Illumination - See Fig 5.
- EVAP Purge System Flow Check - Purge flow from the charcoal canister through the purge valve is monitored after fuel system adaptation is completed and the lambda controller is in closed loop. Diagnosis is started during regular purging, and occurs over 2 steps. See Fig 6.
- Monitoring Cycle Of Evaporative Purge System Flow Check
- 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 the 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 operation, the 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, the diagnosis procedure is completed.
To start diagnosis function (step 2) several conditions have to be satisfied:
- Vehicle speed = 0
- Engine at idle speed.
- Closed loop of lambda controller.
- Coolant temperature greater than a fixed limit.
- Engine idle speed variation greater than a fixed limit.