Apparatus, method and system for diagnosing reductant deposits in an exhaust aftertreatment system

An exhaust gas treatment system for an internal combustion engine has a reluctant delivery system that delivers reductant to an exhaust stream in an exhaust aftertreatment system. A temperature sensor is positioned in or near the flow of reductant and exhaust to measure the temperature of the reluctant and exhaust. A change in temperature over time, such as an increase, decrease, or change in variation amplitude, indicates the presence of a reductant deposit in the system. Detection of the deposit initiates a regeneration cycle in which the operating characteristic of the system change to eliminate the reductant deposit to present it front hindering the performance of the exhaust aftertreatment system.