Patent ID: 8484949

Claim:
A method for monitoring of an after treatment injector (ATI) located in an exhaust gas system of an internal combustion engine, the exhaust gas system comprising: an exhaust gas purification unit, an after treatment substance injection system (ATSIS) including a) the ATI for injection of a substance into the exhaust gas system, b) a conduit for supplying of the substance from a container to the ATI, c) a pressure sensor located in or near the ATI in such a way it will sense a pressure of the substance in the ATI, d) an electronic control unit (ECU) for control of the ATI, and e) a flow regulator which controls the flow in the conduit for the conduit for supplying of the substance from a container to the ATI, and an on board diagnosing (OBD) system which is connected to the ECU and the pressure sensor, either directly or via the ECU, the OBD being provided with comparative data for deciding functionality of the ATI in order to detect abnormal functionality of the ATI, the method comprising suspending normal operation of the ATI and initiating a control sequence for monitoring functionality of the ATI, the control sequence comprising performing, via the ECU, the following sequential steps: I. setting the flow regulator to open and setting the ATI to be closed, II. closing the flow regulator and keeping the ATI closed, III. keeping the flow regulator closed and opening the ATI, IV. keeping the flow regulator closed and closing the ATI without opening the flow regulator before closing the ATI, and V. opening the flow regulator to open and keeping the ATI closed, performing, via the OBD, a frequency analysis of measured pressure values detected by the pressure sensor during performance of the predetermined sequence of opening and closing commands and preparing a pressure curve with the measured pressure values.