DETROIT (AP) — Federal regulators are investigating whether Ford Motor Co. should expand a 2013 safety recall of diesel trucks.

The previous recall involved 2,951 F-350, F-450 and F-550 trucks sold with ambulance packages. The trucks were equipped with 6.7-liter diesel engines that could stall because of a malfunctioning sensor. Ford replaced the sensors for free.

But since then, the National Highway Traffic Safety Administration says it has received complaints from truck owners who didn't have the ambulance packages as well as owners who got the first repair.

The government is now investigating to see whether the first recall repair worked, and whether Ford should expand the recall to cover all of the 200,000 diesel-equipped trucks it sold from the 2011 and 2012 model years.

Ford spokeswoman Kelli Felker says the company is cooperating with the investigation.