COMPETENCY DIAGNOSIS SYSTEM FOR UREA WATER TEMPERATURE SENSOR

Provided is a competence diagnosis system for a urea water temperature sensor that can limit a diagnosis during a cold start. A competence diagnosis system for a urea water temperature sensor 129 includes a competence diagnosis unit 127 that diagnoses a failure of a temperature sensor 121 provided in a urea tank 105 by comparing a temperature of urea water measured by the temperature sensor 121 with an ambient temperature. The competence diagnosis system for a urea water temperature sensor 129 includes a cold start condition determination unit 128 that obtains a difference between an engine cooling water temperature and an ambient temperature, a difference between an engine cooling water temperature and a fuel temperature, and a difference between an ambient temperature and a fuel temperature by using an engine cooling water temperature, an ambient temperature, and a fuel temperature measured immediately after engine starting, and allows a diagnosis by the competence diagnosis unit 127 when the temperature differences are less than or equal to a predetermined threshold value.