A lawsuit claims General Motors Co. fixed a defective part on police versions of the Chevrolet Impala but didn't correct the same problem in hundreds of thousands of other Impalas.

The class-action lawsuit, filed last week in Detroit, says 2007 and 2008 model-year Impalas have defective spindle rods, which connect the suspension to the rear wheels. The defect misaligns the wheels, which makes the tires wear out faster.

According to the lawsuit, GM told dealers to replace the spindle rods and tires on affected police vehicles. It also authorized dealers to reimburse police who had purchased replacement tires.

But the suit says GM didn't offer the same remedy to non-police owners. The company sold 423,000 Impalas from those model years.

A GM spokesman was not immediately available to comment Tuesday.