Exhaust gas purification control device

An exhaust gas purification controller applied to an exhaust gas purification system including a catalyst of a selective reduction type provided in an exhaust passage of an internal combustion engine, a supply valve provided to supply urea water to an upstream part of the catalyst in the exhaust passage, and a pump for pumping the urea water to a supply passage connecting a urea water tank for storing the urea water with the supply valve, the exhaust gas purification controller for performing an abnormality diagnosis of the supply valve, the exhaust gas purification controller configured to:

• drive the pump at a start of operation of the exhaust gas purification system to start filling the supply passage with the urea water;
• output a valve opening command for opening the supply valve when a urea water pressure in the supply passage exceeds a predetermined valve opening pressure after filling the supply passage with the urea water is started;
• determine presence or absence of a sticking abnormality of the supply valve based on the urea water pressure after the output of the valve opening command;
• and
• determine that the sticking abnormality of the supply valve has occurred when an increase amount of the urea water pressure during a predetermined period from the output of the valve opening command is larger than a predetermined threshold.