The automaker said it was looking for a fix but did not say whether it planned to issue a formal recall for the 2010 model year Lexus GX 460. It has stopped selling the SUV and has temporarily idled the vehicle's Japanese production line.
Federal regulations give an automaker five days, after finding that one of its vehicles is not in compliance with safety standards or has a defect, to make a report to the U.S. Transportation Department. A spokeswoman for the National Highway Traffic Safety Administration said the agency was aware of Toyota's test results and was waiting for the automaker's formal report.
This week, NHTSA issued an advisory asking motorists to use caution when driving the vehicle.
Separately, Toyota said Friday that it would launch a voluntary recall involving about 600,000 Sienna minivans sold in the U.S. to address potential corrosion in the spare-tire carrier cable.
The automaker said the condition affects some 1998 through 2010 Siennas that have been operated in cold-climate areas with high use of road salt. This could let the spare tire fall from the van, creating a danger for vehicles following it.
Toyota said it was working on a fix, but for now it wants owners to bring the vans to a dealership for an inspection. Once it has a remedy, owners will get a second notice advising them of the solution.
In its report on the GX SUV on Tuesday, influential buyers guide Consumer Reports said that "when pushed to its limits on a handling course" on the magazine's test track, the rear of the Lexus GX "slid out until the vehicle was almost sideways" before the vehicle's electronic stability-control system was able to regain control.
Lexus spokesman Bill Kwong said Friday that engineers started testing the Lexus SUV on a track in Japan on Wednesday, using conditions similar to the Consumer Reports test, and replicated the sliding under certain conditions.
Toyota engineers "are currently evaluating current remedies or fixes. It is too early to speculate what the remedy will be and the timing of the release," Kwong said.
"It is too early to tell if we are going to recall the vehicles. We have to figure out why it is doing it. We have to take it one step at a time," he said.
Consumer Reports and others have said they expected Toyota to modify the software that manages the GX's electronic stability-control system, but Toyota executives said they were evaluating a variety of factors that might cause the vehicle to slide under certain conditions and have not settled on a solution.
The GX, which sells for about $52,000, has been on the market for about three months. About 5,000 vehicles have been sold.
Owners worried about the safety of the vehicle should take it to their dealership, where they will be provided with a loaner "until the issue is resolved," Kwong said.
Morris Grossblatt, 81, a retired auto repairman in Tarzana, said his new GX 460 has been for the most part "an absolute delight."
But the news that Toyota has confirmed rollover concerns has him worried -- but not for his safety.
"I'm always concerned if there could be an accident, but I don't drive in an extreme way and the car has just behaved beautifully," he said. "But I don't like this going on because even though I plan on keeping it for many years . . . my $70,000 car won't be worth much as a trade-in."
He also worried that his insurance company might increase his premium.
The vehicle's sales suspension comes as Toyota is using aggressive financing and lease incentives to entice customers back to showrooms after a series of large recalls and federal probes into safety defects.
The Japanese carmaker has issued nearly 10 million recall notices worldwide in recent months for problems related to sudden acceleration that it blames on sticky gas pedals and faulty floor mat design, as well as braking problems in some hybrid models.
The latest safety issue "is a huge problem, but the real question is how much longer is this going to go on?" said Jeremy Anwyl, chief executive of Santa Monica-based Edmunds.com. "If three months from now we haven't heard anything else, Toyota can start to regroup and move on."
Toyota's brisk sales last month have continued into April, demonstrating that despite the ongoing controversies, the automaker has a "decades-old reservoir of good will" that is helping it through the crisis, Anwyl said. "One could argue that with all this news, why would anyone buy a Toyota?"
Toyota has until Monday to decide whether to contest a $16.4-million fine levied by the U.S. Transportation Department -- the largest ever sought by the agency from an automaker. The government accused Toyota of delaying before issuing the recalls.
Times staff writer Tiffany Hsu contributed to this report.