Software Bugs Threaten Toyota Hybrids

Heading home from work in late March, Diana Len’s heart raced as she tried to figure out what was happening to her normally reliable 2004 Toyota Prius. The St. Augustine, Fla., resident was boxed in between several other vehicles in heavy traffic when a big red triangle suddenly appeared on the dashboard. Then, the check-engine warning light came on, along with the cryptic letters “VSC,” or vehicle stability control.

The next thing Len knew, the vehicle’s gasoline-powered engine shut off.

Luckily, the Toyota hybrid—which runs on both gasoline and electricity—had enough juice in its batteries to get Len to a nearby parking lot where she could call a tow truck. Len’s vehicle spent the next week in the service shop at Lighthouse Toyota in St. Augustine before the problem was eventually traced to faulty software and not the vehicle stability control, the systems that prevent a vehicle from tipping on sharp turns.

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“It all sounded a bit mysterious to me,” says Len, whose vehicle’s repairs were covered under a warranty. “I had no idea it would be that complicated or take that long to repair.”

Nor, as it turns out, did a number of other Prius owners.

In what is a rare black eye for the Japanese automaker, the National Highway Traffic Safety Administration opened an investigation into the hot-selling vehicle to determine whether a safety recall is warranted.

Toyota has issued service bulletins, asking 2004 and 2005 Prius owners to bring their vehicles into dealerships to have the hybrid electronic control unit reprogrammed to eliminate an error that could cause the vehicle to limp along as though it has run out of gas.

But what is causing the vehicles to stall? In its initial investigation, Toyota said on July 22 it believes that almost half of the 67 complaints received by NHTSA are related to an error in software involving the hybrid electronic control unit. When functioning properly, the control unit allows the vehicle to smoothly shift between its electric motor and gas engine. It is still investigating the remaining cases, but “due to the limited amount of information surrounding the incidents” it was having difficulty determining the exact cause.

Toyota spokeswoman Allison Takahashi says the service bulletin, first issued in October 2004, will fix the software error.

While the problems do not seem to have dented Prius sales—Toyota says the vehicle is on target to more than double sales in 2005—the incidents raise questions about the quality of software increasingly being embedded in today’s vehicles. Embedded software now controls some of a car’s most critical operations, including engine performance, air bags, steering, anti-lock braking systems and stability control systems.

If Toyota, which consistently tops vehicle quality surveys, can’t get it right, how bad is the rest of the industry?

  • Story Guide:
    Software Bugs Threaten Toyota Hybrids
  • A Costly Problem
  • Computer on Wheels
  • Toyota Motor Sales USA at a Glance

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