An engine system includes a diesel engine having an exhaust manifold connected to the diesel engine. An exhaust passage is connected to the exhaust manifold and a diesel particulate filter is disposed in the exhaust passage. An air intake passage is provided for supplying fresh air to the diesel engine. A bypass passage is connected between the air intake passage and the exhaust passage in a location downstream of the diesel particulate filter. The bypass passage includes a bypass control valve for opening and closing the bypass passage during a diesel particulate filter regeneration cycle when the vehicle is at low speed or idle.