Prius Brakes: Adding Straw to Toyota's Load

(MoneyWatch)  The last thing Toyota needs right now is another challenge to its product quality, especially when the car in question is the company's third-biggest seller, which has so far mostly ridden above the sudden acceleration fray. Toyota's prestige product, the hybrid Prius, has minor floormat issues, but was not included in the company's massive "stop sale" affecting eight popular models.

But on Wednesday, the Japanese government ordered Toyota to investigate the Prius for brake-related problems. Specifically, Kenji Sato, a Japanese transport ministry official in charge of recalls, said there have been 14 complaints about Prius brakes, which seem to have a problem at low speeds when surfaces are slippery.

Is this problem related to sudden acceleration? It's possible they both are, at heart, electronic interference issues, since the Prius uses a "brake by wire" technology with parallels to the "throttle by wire" technology now being investigated by federal car safety officials for interference issues. Toyota has actually been in the vanguard (with Mercedes) in developing brake-by-wire.

The complaints center on the third-generation Prius introduced for the 2010 model year (on sale in Japan last May). One Japanese report said a Prius with failing brakes had run into another car at an intersection last July, injuring two. And there have been 77 other complaints since the new model went on sale.

It's not just in Japan. The National Highway Traffic Safety Administration (NHTSA) maintains an online inventory of complaints, and the file on 2010 Prius brake problems is large. There's a real pattern: People say their brakes exhibit symptoms after they hit potholes. Here are a few complaints recorded on NHTSA's site:

"The 2010 Toyota Prius exhibits brake failure and sudden acceleration while slowing down on bumpy roads," reports an owner. "For example, if you're slowing down towards a red light, and then all of a sudden you hit a pothole, the car will suddenly accelerate and may cause a crash with the person ahead of you!"

Here's another: "I have a 2010 Prius. When I hit a pothole while stepping on the brake, the brakes let go. I have to rebreak (sic). The car actually seems to speed up. It is very frightening. I have taken it to the dealer. They say it is the anti-lock brakes. I have had anti-lock brakes before and never have had that kind of problem."

One more: "I purchased mine [a 2010 Prius] in July, and since then have experienced four instances of this problem. In each case, I was decelerating with the brakes steadily applied and rolled over a bump or pothole in the road. At that moment, the brakes stopped working, or the braking power was severely reduced, and the car felt as if it lurched forward."

There are further incidents reported at the PriusChat forum, under the "braking problem" heading. "If you go over a large bump in the road like a misaligned concrete crack...it feels as though the car almost speeds up for a second before braking," says "Eglmainz."