Consumer Reports has announced a rare “Do Not Buy” rating for the Lexus GX460 sport utility vehicle. While performing a standard handling test, CR found that the GX460’s electronic stability control was extremely late to intervene.

The maneuver tests for a condition called ‘lift-throttle oversteer’ which is the tendency for a vehicle to fishtail when a driver steers the vehicle into a turn and then lifts off the accelerator pedal suddenly. Drivers in the real world may face this same condition if they veer onto a highway exit ramp too quickly and then try to slow.

The Lexus GX460, which is mechanically similar to the Toyota 4Runner, comes standard with an electronic stability control system that is supposed to detect a slide and then carefully activate the brakes to help the driver regain control of the vehicle.

Consumer Reports found that the electronic stability control system in the GX460 was extremely late to intervene. So much so that the vehicle was almost completely sideways before the system activated.

Curiously, the Toyota 4Runner had no such issue when it was run through the same test by Consumer Reports.

The magazine notes that in the real world, a GX460 may come into contact with a curb or slide off the pavement, which may “trip” the vehicle and cause a dangerous rollover crash. CR notes that ‘tripping’ is the number one cause of rollover crashes.

Consumer Reports goes to great lengths to remain objective, even purchasing its test vehicles from dealerships anonymously, so as to avoid foul play. (It’s rare for a manufacturer to specially-prepare test vehicles for the media, but several enthusiast magazines have reported this happening in the past.)

The magazine tested their own GX460 and then paid Lexus to borrow a second vehicle from the media test fleet. Tests on the second vehicle produced the same fishtailing outcome.

For its part, Toyota’s luxury division is responding quickly. Lexus has announced a stop-sale for all GX460 models and is offering free loaner cars to its affected customers. The company states that its, “extensive vehicle testing provides a good indication of how our vehicles perform and we are confident that the GX meets our high safety standards.”

Nonetheless, the company has dispatched engineers to investigate the claim and potentially develop a fix.

For embattled Toyota, this is the latest in a long string of serious safety issues and the price tag for recalls, government fines, lawsuits, and lost consumer confidence is likely to continue climbing.