DETROIT (AP) -- U.S. safety regulators are investigating whether older-model Ram pickup trucks with manual transmissions can be started without the clutch being depressed.

The probe covers about 110,000 Ram 2500 and 3500 pickups made by Chrysler from the 2004 through 2006 model years.

Ap Ram Truck

A 2006 Ram 3500 SLT Mega Cab four-wheel-drive pickup truck. (AP file photo/David Zalubowski)

The National Highway Traffic Safety Administration said in documents posted on its website Friday that it has three complaints about the problem, including one fatal accident. In that case, a child was able to start a truck without using the clutch. The truck moved forward, striking and killing another child, the safety agency said.

Vehicles with manual transmissions are required to have interlock mechanisms that stop the motor from being started unless the clutch is depressed.

"The clutch interlock safety switch had not been tampered with and was in its original condition," the truck owner wrote in the fatal accident complaint. "The switch has been tested and found to be defective."

People who file complaints with NHTSA are not identified. The complaint was filed on Feb. 26, and the crash happened on Aug. 25, 2013. It involved a 2006 Ram 3500 heavy-duty pickup, according to the complaint.

In another case, a truck engine was cranked without the clutch being pressed, and it moved forward and struck a person working under the hood. The person was knocked to the ground but not hurt, according to the documents.

The investigation was opened May 19, according to documents posted by the agency on Friday. An investigation can lead to a recall, but so far none has been issued.

Chrysler said in a statement that it is cooperating in the investigation. The company said that customers with concerns about their trucks should contact their dealer.

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