| Tank leak diagnostic system |
| The tank leak diagnostic system detects leaks in the entire fuel system, including the fuel tank, activated charcoal filter and activated charcoal filter solenoid valve 1 -N80-. |
| The mechanical components of the tank leak diagnostic system consist primarily of a vacuum-driven diaphragm pump, with a reed contact located on the operating rod of the pump diaphragm. The vacuum required is supplied to the pump from the mechanical vacuum pump or from the engine intake. |
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| The diaphragm pump delivers a pressure of 20 ... 30 mbar to the fuel system when the tank leak diagnostic system starts up. In this condition the pump diaphragm is extended, so the reed contact located on the operating rod is in the „open“ position. |
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| The diagnostic system detects whether the reed contact remains open for 15 seconds. In this case the fuel system is free of leaks. |
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| If the pressure drops (indicating a leak), the diaphragm returns and the reed contact closes. |
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| If the reed contact closes within 15 seconds, a further test is performed. The diaphragm pump is then activated for another 4 strokes. For each of these strokes the engine control unit measures the period of time it takes for the reed contact to close again after pressure delivery. In this way the control unit can distinguish between a „small leak“ (smaller than 1 mm diameter) and a „large leak“. |
| The automatic diagnosis function is activated shortly after every cold start (below 35°C) when the vehicle reaches a constant speed above 10 km/h. Any faults detected are stored in the memory. A fault message is displayed in the instrument cluster if the fault is detected during two consecutive road trips. The diagnosis function can also be activated with the vehicle diagnostic, testing and information system -VAS 5051B- → Chapter. |
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| The diagnosis can be repeated up to 10 times during the first 20 minutes after a cold start. |
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| By selecting measured value block 071 with vehicle diagnostic, testing and information system -VAS 5051B- connected, you can see whether the automatic tank leak diagnosis is being performed → Chapter. |
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