Evaporative Purge System Monitoring
Evaporative System Leak MeasurementGeneral Description of Leak Measurement
The evaporative system monitoring permits the detection of leaks in the evaporative system with a diameter of 0,5 mm and up.
By means of a DiagnosticModul TankLeakage (DM-TL), an electrical actuated pump located at the atmospheric connection of the evaporative canister, a pressure test of the evaporative system is performed in the following order:
a) During the Reference Leak Measurement, the electrical actuated pump delivers through the reference restriction. The engine-management system measures the pump's electrical current consumption in this section.
b) During the 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 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 leak measurement is a measure for the leakage in the tank.
c) After the test the remaining pressure in the evaporative system is bled off through the charcoal canister by switching off the pump and solenoid.
Monitoring Structure of Leak Measurement
Diagnosis Frequency and MIL illumination
Diagnosis Frequency and MIL illumination: No refueling detected; leak > 10 mm
Diagnosis Frequency and MIL illumination: After refueling detected; leak > 0,5 mm
Evaporative Purge System Flow Check
The 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. The diagnosis is started during regular purging.
Monitoring Process 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 or 1st step fails
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.
If a predetermined value is reached the diagnosis procedure is completed.
Step 3 - For stoichiometric mixture or 2nd step fails
If the threshold at the 2nd step is not reached an additional procedure is performed. The purge valve is opened and the idle air control valve simultaneously is closed to compensate the idle speed increase. The effect is a decrease of the measured idle air mass by the mass air flow sensor.
If a predetermined value is reached the diagnosis procedure is completed.
Monitoring Structure of Evaporative Purge System Flow Check