The federal government has reopened and expanded an investigation into Honda Motor Co.'s CR-V sport-utility vehicle, trying to determine why 2003 and 2004 models sometimes catch fire shortly after their initial oil change.

The problem has persisted more than two months after the National Highway Traffic Safety Administration closed a preliminary investigation into the fires and related oil leaks in July. At that time the agency agreed with Honda that the incidents were mostly likely caused by faulty work by service technicians.

The new inquiry puts the focus back on the manufacturer. Called an "engineering analysis," the probe is the most serious level of inquiry conducted by NHTSA's Office of Defects Investigation. Such investigations lead to vehicle recalls roughly 60 to 80 percent of the time, an agency spokeswoman said.

Honda has been working to notify its dealers and service technicians about ways to avoid the problem since mid-July, but continuing reports of new incidents draw "into question the effectiveness of the service communication," NHTSA said in the official notice of investigation.

The agency declined to comment further, saying it is against policy to talk about ongoing investigations.

A Honda spokesman said the company would cooperate with NHTSA and is continuing to conduct its own probe. "We continue to turn over every stone to ensure there isn't something else that's a contributing factor, in terms of the materials or workmanship," Honda spokesman Andy Boyd said. "To this point we've not been able to identify any defect or other factor, other than the issue at the dealer level."

The company said the problem seems to be caused by technicians, usually at dealerships, improperly changing the oil filter during a CR-V's initial oil change, usually at 5,000 miles or less. The rubber gasket from the factory-installed filter often sticks to the engine block, and when the new filter is installed over it, the new filter fails to seal well, and oil leaks out. The oil sprays onto the CR-V's hot manifold and ignites.

Honda says it does not know why the old gasket is so likely to stick to the engine block or why the 2003 and 2004 model CR-Vs are more prone to this than other model years or other vehicles. Honda said the company has found no design changes from earlier model years that would explain why the fires have occurred in the more recent models.

NHTSA and Honda have identified 71 related incidents involving both model years, 44 of which resulted in fires. There have been no injuries reported, but a significant number of the fires consumed the whole vehicle. While the number of complaints is a small portion of the total estimated 280,000 such vehicles on the road, experts say the problem's severity and mysterious origins make it especially troubling.

Honda does not believe news of the fires has scared away potential CR-V buyers, Boyd said, but sales of the small SUV were down slightly in both July and August compared with the same months last year, according to Ward's AutoInfoBank.

Several Honda dealers say they dislike being blamed by the manufacturer, pointing out that an occasional lapse in an oil change doesn't lead to such potentially catastrophic results in other vehicles. Michael Shockley, general manager of Shockley Honda in Frederick, said his dealership has had two CR-V fires, one last year and one last month, involving different mechanics.

"The whole shop goes on red alert and -- BAM! -- it happens again," Shockley said. "When you burn two cars you must apologize to the owners of those cars; it's kind of a horrible thing to do, right? But in both cases the customers looked at me and said, 'Please don't fire that mechanic, I don't think it was his fault.' The customers felt it was the fault of Honda."

The problem, which has lit up online Honda chat groups, aims at the heart of Honda's reputation as one of the safest and most consumer-friendly of car companies, said Bob Kurilko, an auto marketing expert at Edmunds.com. "The publicity of a [possible] forced recall is not good, especially for Honda, because they have a pristine reputation and want to manage that and protect it," he said. "Honda acting quickly could jump in front of this thing and just initiate a voluntary recall, and I think they're going to want to do that before NHTSA forces them."

But Boyd, the Honda spokesman, said the company believes a recall would be counterproductive based on current understanding of the problem.

Recalling the vehicles to replace oil filters "wouldn't accomplish anything," he said. "You'd still have a certain percentage having an oil leak or fire. It's not that different than the issue running its course."