A preliminary investigation two years ago by the U.S. National Highway Traffic Safety Administration into whether older model Jeeps are at risk for fires has been recently expanded, prompting a new level in the probe that makes it likely that around 5.1 million vehicles could be recalled soon.

The NHTSA is looking into whether Chrysler Group Jeep vehicles could catch fire after rear-impact accidents, reports Reuters. The investigation includes around 3 million 1993-2004 Jeep Grand Cherokee SUVs, 1.1 million 1993-2001 model year Jeep Cherokee SUVs, about 975,000 2002-2007 Jeep Liberty SUVs.

The NHTSA raised the level of its probe, which began two years ago, to an engineering analysis and expanded it to include the other Jeep SUV models mentioned.

Chrysler’s liaison with federal regulators says that the risk of fire isn’t any higher in those three models than in similar models from other car makers.

“The vehicles are absolutely safe,” he said in an interview.

But the NHTSA said today: “NHTSA’s assessment of the data collected during preliminary evaluation indicates that rear-impact-related tank failures and vehicle fires are more prevalent in the Jeep Grand Cherokee than in the non-Jeep peer vehicles.”

It’s not quite a recall yet, but with this new level of investigation, it could mean that officials just want to make sure they’ve got every angle covered before asking for the manufacturer to issue a recall.

The investigation was prompted in 2010 when a consumer watchdog group said that the fuel tank storage system in Grand Cherokees was defective, and because its fuel tank is behind the rear axle, the risk of fire could be increased after a crash.

U.S. expands fire risk probe of older Jeep models [Reuters]

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