(AP) - U.S. safety regulators have expanded an investigation into 23 complaints of fires in Jeep Wrangler SUVs. The National Highway Traffic Safety Administration hasn't figured out what caused the fires, but it's asking carmaker Chrysler for information on Wranglers from the 2007 through 2012 model years. When it began March 28, the probe centered on vehicles from the 2010 model year.
The classic Wrangler is among Chrysler's more popular models. Chrysler sold more than 532,000 Wranglers from 2007 through March. It's unknown how many are affected by the investigation.
The probe comes at a critical time for Chrysler, which has had quality problems in the past but showed improvement in an annual study by Consumer Reports magazine. The company, which is majority owned by Italian automaker Fiat SpA, is making a remarkable comeback from its 2009 bankruptcy and restructuring. It posted a net profit last year for the first time since 1997.
NHTSA said on its website Wednesday that it has received 23 complaints about fires in Wranglers from the six model years. Four people were hurt, including three who received minor burns and one whose injuries were not explained in the complaints. Two houses were damaged.
The safety agency is focusing on overheated transmission fluid and electrical wiring as possible causes. It has asked Chrysler for information about allegations of smoke or fire in Wrangler engine compartments. The company has until May 22 to respond. It's common for the agency to expand investigations to include similar vehicles. The investigation could lead to a recall, but there isn't one yet.
Chrysler spokesman Eric Mayne said in an e-mail that the company was aware of a small number of fires in Wranglers and is cooperating with the investigation. Vehicle fires, he says, are complex and can occur for many reasons unrelated to the vehicle's design and manufacture.
"Poor maintenance, improper vehicle use or installation of aftermarket equipment often are causes of vehicle fires," he says.
In one of the complaints NHTSA received, the owner of a 2007 Wrangler said it caught fire in a driveway on Feb. 15 and exploded, setting the nearby house on fire. Another owner said a 2009 Wrangler was sitting in a garage on March 10, 2010, when its engine compartment caught fire, destroying the Jeep and damaging the home to which the garage was attached.
The owner of a 2008 Wrangler reported smelling something burning while driving 55 mph. After the owner pulled over, the Wrangler was quickly engulfed in flames. The driver and two passengers had minor burns to their faces and arms, according to the complaint. Firefighters put out the flames and told the owner that transmission fluid boiled into the engine and transmission, causing the fire.
NHTSA announced the investigation on April 1 involving 2010 Wranglers.
The safety agency also is investigating reports of engine fires in the Chevrolet Cruze small car from the 2011 model year.