Method and arrangement for monitoring of injector

A method for monitoring of an exhaust gas purification system for an internal combustion engine, the system comprising:

• An exhaust gas system comprising an exhaust gas purification unit
• An After Treatment Substance Injection System (ATSIS) including
• a) An After Treatment Injector (ATI) for the injection of a substance into the exhaust gas system, the ATI located in the exhaust gas system upstream of the exhaust gas purification unit,
• b) A conduit for supplying of the substance from a container to the ATI
• c) A flow regulator for controlling the flow in the conduit of the substance from the container to the ATI
• d) A pressure sensor located downstream of the flow regulator
• e) An Electronic Control Unit (ECU) for control of the flow regulator and the ATI
• an On Board Diagnosing (OBO) system which is connected to the ECU and a pressure sensor connected to the OBO, either directly or via the ECU, the OBO provided with comparative data for the functionality of the After Treatment Substance Injection System (ATSIS) in order to detect abnormal functionality of the ATSIS
• the ECU (10) is programmed to perform a predetermined sequence of opening and closing commands for the flow regulator and the ATI in order to monitor the functionality of the flow gas regulator, the ATI and the pressure sensor, where outputs values from the pressure sensor is compared with said the comparative data in order to determine which one of the flow regulator, ATI or pressure sensor is malfunctioning, wherein the method comprises performing, via the ECU, the following sequential steps:
• I. setting the flow regulator to open and set setting the ATI to be closed,
• II. closing the flow regulator and keep keeping the ATI closed,
• III. keeping the flow regulator closed and open opening the ATI,
• IV. keeping the flow regulator closed and slew closing the ATI, and
• V. opening the flow regulator to open and keeping the ATI closed.