Leak Diagnostic Unit

Courtesy of VOLVO CARS CORPORATION

The function of the leak diagnostic unit is to pressurize the fuel tank system during leak diagnostics and to open the fuel tank system to the surrounding air during evaporative emissions control.

The leak diagnostic unit consists of a plastic housing with: 

1. electrical air pump
2. a valve / solenoid which governs the air flow in the unit
3. a heater element (PTC resistor) which warms up the pump.

The electrical pump, valve and heater element in the unit are supplied with voltage by the system relay. The pump, valve and heater element are grounded (control) in the engine control module (ECM).

During leak diagnostics the pump in the leak diagnostic unit starts. The valve in the unit is operated by the engine control module (ECM) by grounding the different circuits internally in the engine control module (ECM). Operation depends on whether the diagnostic phase is checking for leakage or checking the function of the diagnostic system. The engine control module (ECM) gauges the power consumption of the pump during pressurization. The power consumption corresponds to a certain pressure in the fuel tank system. See also: LEAK DIAGNOSTICS (CERTAIN MARKETS ONLY)

The engine control module (ECM) can diagnose the leak diagnostic unit.

The valve in the leak diagnostic unit can be activated and the power consumption of the pump can be read off.

The leak diagnostic unit is at the upper front edge of the fuel tank.