updated 9/30/2009 7:00:01 PM ET 2009-09-30T23:00:01

Federal investigators said of the 102 accidents caused by stuck gas pedals on Toyota vehicles, there are four possible causes involving the floor mats: The mats are too long or too thick, they weren't properly secured, the gas pedal design is flawed or the floor geometry is defective.

The wide array of causes presents a challenge to Toyota engineers who are trying to come up with a way to fix the problem that is leading to a recall of 3.8 million vehicles, including the Camry, the top-selling car in the U.S.

"We've evaluated a number of different years, makes and models of Toyota and don't believe that there is a one-size-fits-all answer as to why these incidents are occurring," said National Highway Traffic Safety Administration spokesman Rae Tyson on Tuesday. "I think Toyota is going to have a challenge on its hands to come up with a remedy that is going to address the problem."

Toyota spokesman John Hanson acknowledged the problem is more complex than vehicle floor mats alone, but involves the way the floor mat interacts with other parts of the vehicle.

"Other factors may be coming into play here," he said. "That's why we feel that probably the remedy could be different from vehicle to vehicle."

On Tuesday, the Japanese automaker issued a safety advisory urging owners of 3.8 million car and trucks — including popular models like Camry, Prius and Tacoma — to remove driver-side mats. It wants drivers to watch out for loose or incorrect mats that could slide out of position and cover pedals.

Toyota is still studying the problem. Once it comes up with a fix, it will issue a recall of the models. It will be Toyota's largest-ever U.S. recall, accounting for about 15 percent of all the automaker's vehicles on U.S. roads, the company said.

The safety advisory was prompted by an accident last month killing four people near San Diego. In that incident, a floor mat trapped the gas pedal on a 2009 Lexus ES 350, causing it to accelerate out of control, strike an SUV, launch off an embankment, and burst into flames.

NHTSA said it had received reports of 102 incidents in which the accelerator may have become stuck on the Toyota vehicles involved. The problem has led to 13 crashes, 17 injuries and 5 fatalities in Toyota vehicles, according to NHTSA.

Toyota's warning affects 2007-2010 model year Toyota Camry, 2005-2010 Toyota Avalon, 2004-2009 Toyota Prius, 2005-2010 Tacoma, 2007-2010 Toyota Tundra, 2007-2010 Lexus ES350 and 2006-2010 Lexus IS250 and IS350.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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