Winter Weather Warning for Prius Drivers

Traction control shuts down engine on slippery surface

One year after first reports in that the Toyota Prius traction control system can fail to operate properly on a snowy road, Prius owners report the hybrids TRAC system is still inadequate on slippery inclines.

One Vermont Prius driver, suffering through a recent January snowfall, described Toyota Prius traction control as "dangerous in mountainous snow country.

The Vermonter wrote that the system is flawed and should definitely be modified. In marginal traction conditions, such as Vermont winters, the Prius traction control system will shut down power to the drive wheels and prevent forward movement.

In January 2007, reported the traction control failure in the Prius as one of the oddest Prius stories on file.

"When my car is on any kind of slick surface that causes one of the front wheels to slip, all power to the drive system is stopped," wrote Christopher of Reston, Virginia.

Traction control failure in the Prius is no longer a isolated event. The continuing failure is producing damaging results.

A Langley, Washington Prius owner told us that her hybrid this month stopped totally on a medium uphill approach to her driveway and garage resulting in the car falling off (the) driveway into ravine of trees on a snowy December day.

In Medford, Oregon, Mike is the most recent victim of the reluctant traction control system.

I am a seasoned driver in the snow. I can drive front-wheel drive, rear-wheel drive and four-wheel drive. I am a forester and have been driving in snowing conditions for 28 years, 22 of those years on the job," he wrote. "I just had my first experience driving my Toyota Prius in the snow today. The engine cut out all power anytime the wheels slipped at all.

"Very dangerous"

Mike said that the traction control failure made driving the vehicle on an uphill climb almost impossible.

It was very dangerous as you had no control as other vehicles came toward you, and once I lost momentum and could not start again. This was in 2 inches of wet snow on a 6 percent incline. I finally inched my way home and ended up putting chains on to back into my flat driveway with 2 inches of wet snow, he wrote.

He concluded that the traction control system in the Prius is absolutely a design flaw.

It is just a matter of time before someone is injured, killed or stranded because of the car's performance in the snow. It's too bad because I have really enjoyed the car up until now. he said.

In Milwaukee, Wisconsin, Andrew owns a 2006 Prius with the hesitating traction control.

It has a very serious design flaw which Toyota denies and refuses to fix, Andrew wrote. In slippery conditions, if there is any wheel slippage, the car shuts down all power to the wheels leaving you without any control. When pulling out into traffic, power to the wheels just dies if it's slippery, especially in snow and leaves you helplessly exposed to oncoming traffic.

Andrew wrote that he is afraid to drive it in anything less than perfect conditions. His car is not able to climb a hill in the snow and as a result, other cars pass him on both sides my car refuses to apply any power to the wheels.

People are going to get killed, Andrew warns.

Toyota's response

Toyota spokesman Bill Kwon agreed last year that the traction control system in the Prius could impact performance in snow conditions but he insisted that the system is not a safety problem.

"Prius has TRAC (traction control) as standard equipment," he said. "The purpose of traction control is to help prevent wheel spin and minimize slippage of the drive wheels by applying brakes and/or reducing engine power."

Kwon pointed out last year that an 8- to 10-degree grade "is a fairly steep grade and combined with snow would cause a loss of traction which will activate the traction control system and therefore reduce or cut power."

"A vehicle without TRAC in those conditions," Kwon added. "would probably just start spinning in place and eventually spin out of control. In my opinion, it's better to have the vehicle stop then to have the wheels spinning and out of control."

Toyota did not respond to our request for an update on plans to modify the existing Prius traction control system.

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