Patent ID: 8375702

Claim:
An exhaust emission control system for an engine, comprising: a flow passage adapted to allow an aqueous urea solution for reducing nitrogen oxides contained in exhaust gas of the engine, to pass therethrough; a supply/recovery section including a drive a pump and a selector valve to supply an aqueous urea solution to the flow passage and recover an aqueous urea solution from the flow passage, and a electronic control unit including an algorithm which when implemented performs a process to control the supply/recovery section and, in response to a predetermined stop condition, to automatically stop the engine, and subsequently, in response to a predetermined restart condition, to automatically restart the automatically stopped engine; wherein the electronic control unit programmed to, when the engine is forcibly stopped by turning off an ignition switch, instruct the supply/recovery section to recover an aqueous urea solution from the flow passage, and, when automatically stopping the engine in response to the predetermined stop condition while said ignition switch remains ON, to prohibit the supply/recovery section from recovering an aqueous urea solution from the flow passage.