The National Highway Traffic Safety Administration has opened a preliminary investigation into 2003 model year Ford Crown Victorias after two police fleets reported unusual axle wear on a "significant" number of their police cars, according to a Dow Jones Newswires report.

Four incidents involving rear axle shaft fractures or wheel assembly separation incidents were reported but a spokesman reportedly said the agency doesn't know of any injuries related to the problem.

Dow Jones said the Crown Victoria platform, called Panther, also underpins the Lincoln Town Car and the Mercury Grand Marquis and NHTSA is seeking information from Ford on all three models, accounting for about 287,000 cars.

The news agency noted that about half of the preliminary investigations that are opened are closed without any action taken, and many of those that are upgraded to engineering studies are also closed with no action.

Sales of the Crown Victoria have been down in recent years after reports began surfacing that the cars had a tendency to burst into flames when high-speed vehicles struck the police cruisers from behind, resulting in several lawsuits being filed against Ford, Dow Jones added.

A Ford spokesman reportedly said the company is co-operating with the NHTSA investigation.