Apparatus for diagnosing a post-processing system and a method thereof

An apparatus for diagnosing a post-processing system, the apparatus comprising:

• a first catalyst, an exhaust heat recovery system, and a second catalyst sequentially arranged along an exhaust line;
• a main bypass line branched from the exhaust line between the first catalyst and the exhaust heat recovery system and joining to the exhaust line on a downstream side of the second catalyst;
• an auxiliary bypass line branched from the exhaust line between the first catalyst and the exhaust heat recovery system and joining to the exhaust line between the exhaust heat recovery system and the second catalyst;
• a first bypass valve installed at a location where the exhaust line and the main bypass line join;
• a second bypass valve installed at a location where the exhaust line and the auxiliary bypass line join;
• and
• a controller configured to perform a diagnosis process to determine whether the second catalyst is abnormal, based on a measured efficiency of the second catalyst and a modeling efficiency of the second catalyst, when a diagnosis condition is satisfied.