The U.S. government is investigating whether Ford Motor’s recall of nearly 3,000 heavy-duty diesel trucks, used by ambulance services, should be expanded to all of the trucks the company sold from the 2011 and 2012 model years.

Ford Motor’s previous recall involved 2,951 F-350, F-450 and F-550 trucks, that were part of its “Ambulance Package” and are equipped with 6.7-liter diesel engines that would stall or fail to restart because of a malfunctioning sensor.

While Ford said it had replaced the faulty sensors for free, the National Highway Traffic Safety Administration (NHTSA) said it continued to receive complaints from truck owners, including those who received the first repair, as well as those who did not have the ambulance packages installed in their vehicles, The Associated Press (AP) reported.

The NHTSA said that it is investigating to see whether Ford's first recall repair worked, and whether the company should expand the recall to about 200,000 diesel trucks it sold in 2011 and 2012, AP reported, adding that Ford is cooperating with the ongoing investigation.