(AP) — The government is closing its investigation into older-model Jeeps with fuel tanks that could rupture and cause fires.

The National Highway Traffic Safety Administration asked Chrysler to recall 2.7 million Jeeps last summer. Involved were Grand Cherokees from the 1993 to 2004 model years and Libertys from 2002 to 2007.

NHTSA said the gas tanks can rupture if they’re hit from the rear. At least 51 people have died in fiery Jeep crashes.

Chrysler Group initially refused to recall the vehicles, but then agreed to recall a little more than half of them and install trailer hitches to protect the gas tanks.

NHTSA said Friday it has no concerns about Chrysler’s recall plans. The agency is expected to issue a final report on its investigation in a few weeks.