Supplying Urea-water Solution

A supply of a urea-water solution is required to ensure efficient operation of the SCR catalytic converter.

Once the SCR catalytic converter has reached a certain temperature (calculated by the exhaust gas temperature sensor before the SCR catalytic converter), the metering control system attempts to build up pressure in the metering line.

For this purpose, the metering module must be closed and the delivery pump actuated at a certain speed for a defined period of time.

If the defined pressure threshold cannot be reached within a certain time, the metering module is opened in order to vent the metering line. This is followed by a new attempt to build up pressure.

A reversible fault is stored if a defined number of pressure build-up attempts remain unsuccessful. If the fault is determined in two successive driving cycles, an irreversible fault is stored and the MIL is activated.

This monitoring takes place only once per driving cycle before metering begins. Continuous pressure monitoring begins after this monitoring run was successful.

A constant pressure of the urea-water solution (5 bar) is required for the selective catalytic reduction process. The actual pressure is measured by the pressure sensor in the delivery module and compared with a minimum and a maximum pressure threshold.

A reversible fault is stored if the limits are exceeded for a certain time. If the fault is determined in two successive driving cycles, an irreversible fault is stored and the MIL is activated.

This monitoring run takes place while metering is active.