General Description of Leak Measurement
The evaporative system monitoring permits the detection of leaks in the evaporative system with a diameter of 0.02 inches and up.
By means of a Diagnostic Module_Tank Leakage (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:
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.
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 2.5 kPa. 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.
0.02 inch diagnosis (P-Code 0456):
The first step of the diagnosis is the reference measurement; the result of the pump reference current is stored as shown in Fig 4. After the solenoid switches, the venting system is pressurized as shown in Figure. In the rough leak measurement the rough leak threshold is reached if the leak is smaller than 0.04 inch, and then the small leak measurement phase follows. If the DMTL current reaches in the small leak time the reference current, then the system is tight (leak smaller than 0.02 inch); otherwise, a small leak between 0.02 - 0.04 inches is detected.
0.04 inch diagnosis (P-Code 0442):
The first step of the diagnosis is also the reference measurement; the result of the pump reference is stored as shown in Fig 4. After the solenoid switches, the venting system is pressurized as shown in Figure. In the rough leak phase (time) the pump current must reach the rough leak threshold 1 (rough leak threshold 1 = idle current pump + K1 x (reference current - idle current). Factor K1 is between 0.16 and 0.28 depending on the characteristic current value of the pump (reference current - idle current), this value varies in every pump.
If the rough leak threshold 1 is not reached in the rough leak time, the rough leak threshold 2 must be reached in an additional time, (rough leak threshold 2 = idle current pump + K2 x (reference current - idle current). Factor K2 between 0.60 and 0.80 depending on the characteristic current value of the pump (reference current - idle current).
If the rough leak threshold 2 is also not reached, a leak > 0.04 inches is detected.
Fig 3 shows the typical current of a tight system, a 0.02 inch leak, and a leak > 0.04 inches.
After the test the remaining pressure in the evaporative system is bled off through the charcoal canister by switching off the pump and solenoid.
In the reference measurement phase the current of the DMTL is checked, if the current consumption is smaller than 15 mA a defect pump/motor is detected, and P1448 is stored. If a current consumption of bigger than 40 mA is measured also a defect pump/motor is detected, and the P1449 is stored.
After the reference measurement the electrical solenoid is switched and the venting system is tight. The solenoid is checked by comparison of the reference current and the idle current immediately after the solenoid has switched.
If the difference between the two currents (reference current - idle current) > 2 mA is not reached, the fault code 1447 is stored.
The P 1434 fault code is set, if current fluctuations (caused by humidity in the DMTL) > 1 mA are detected.