Leak Detector: Description and Operation

2048 Construction and operating principle of the tank-leakage diagnostics module (DM-TL)







The diagnostics module consist of an electromechanically driven excess pressure pump as well as a switching valve with an integrated reference throttle. When the switching valve is in the position illustrated (a), the pump delivers fuel through the reference throttle. When in position (b), the pump delivers into the fuel tank system through the active charcoal filter.

When no leakage diagnosis is being carried out, the switching valve remains in position (a). The active charcoal filter can be regenerated via a large flow cross-section. This results in only minor pressure release. This effect is especially favourable for high active charcoal filter regeneration rates. An air cleaner protects the pump, reference throttle and switching valve from soiling.

Furthermore, the regenerative air does not flow through the pump which has a positive effect on the service life.







The Motronic control module measures the respective power consumption of the pump. The result of the comparison of flow rates is the measurement for tank leakage. A leakage the size of the reference throttle exists if the power consumption is equal in both cases. The comparison with the reference throttle renders the procedure independent from the tolerances of the excess pressure pump and from environmental influences.