Since the introduction of more stringent exhaust standards in 2002, Cat's on-highway truck engines have been plagued with emission-control problems. Some of the on-road engines involved in the recall went into Paccar trucks, such as Peterbilt and Kenworth.

"The majority of complaints from the over the road folks with these engines were related to the emissions regeneration system," said one fleet owner, who asked not to be identified in this story.

"Sometimes, the system would not passively regenerate, and the system would plug up and shut down. Often the system got so hot that turbos failed without warning, wire harnesses melted, injectors plugged, manifold bolts were heated to the point they stretched and the exhaust manifold would come loose," the fleet owner added.

Cat ">exited the on-highway engine business in 2008. Earlier this year, the company ">introduced an on-road truck through a joint venture with Warrenville, Ill.-based manufacturer Navistar International Corp.

Engines involved in the settlement include Cat's ACERT line, which was introduced in 2003 for on-road trucks and 2005 for off-road equipment. Those engine models include Cat's C7 7-liter to its C15 15-liter diesel engines. Earlier engines include models 3406E, 3456, 3126 and 3126E.

Equipment owners can contact a Caterpillar dealer to find out if their machine is a part of the recall.

This story was updated on 8/3.