Abstract: A system is provided for reducing detectable hydrocarbons in the exhaust gas of a diesel engine and for retarding the formation of sulfate including a housing having an inlet and an outlet, a first exhaust gas glow passage extending from the inlet to the outlet within the housing, a first catalyst bed positioned within the first flow passage, a second exhaust gas flow passage extending from the inlet to the outlet within the housing, and a second catalyst bed positioned within the second flow passage. Also provided is a valve for directing the flow of the exhaust gas through one of the first and second flow passages, and an electronic control for controlling the valve in response to engine load and exhaust gas temperature such that the exhaust gas is directed through the first flow passage and the first catalyst bed under low engine load and low exhaust gas temperature conditions and through the second flow passage and the second catalyst bed under high engine load and high exhaust gas temperature conditions.