Apparatus for diagnosing a post-processing system

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

• a first catalyst, an exhaust heat recovery system, and a second catalyst sequentially disposed on 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 determine whether at least one of a first temperature sensor, a second temperature sensor, a third temperature sensor, the first bypass valve, or the second bypass valve is abnormal, based on whether a predetermined diagnosis condition is satisfied,
• wherein the first temperature sensor is configured to measure a temperature of an exhaust gas on an upstream side of the first bypass valve, the second temperature sensor is configured to measure a temperature of the exhaust gas on an upstream side of the exhaust heat recovery system, and the third temperature sensor is configured to measure a temperature of the exhaust gas on the downstream side of the exhaust heat recovery system.