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Is the interrupted braking sensation on Betsy's Prius really "normal"?

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Dear Tom and Ray:



Every time I am braking and go over a bump in our 2008 Prius (a frequent occurrence in hilly San Francisco), the anti-lock braking system kicks in. The problem is that when it does so, it feels like the brakes disengage for a second and the car goes faster. Our Toyota dealer tells me this is the way the ABS is supposed to work, and the brakes aren't disengaging -- the computer system is just taking over the braking process. Is this true? It just doesn't feel safe to me. If I had to stop suddenly, I don't feel confident that I'd be able to in this car. Thanks. -- Betsy

TOM: Gee, Betsy, we hate to kick poor Toyota when it's down. But I guess it's only fair. We've been doing it to GM for the past 35 years.

RAY: I know exactly what you're experiencing, Betsy. I recently was testing a different Toyota hybrid, the RX450h, and had the same sensation with the brakes. And it IS disturbing. There's a moment there where you feel like your brakes are failing.

TOM: Toyota tells us, just like it told you, that this is normal, and not a problem. It says that the ABS system works by momentarily interrupting the braking force to prevent a skid -- and the resulting loss of control.

RAY: And that's true. But most ABS systems interrupt the braking force for a fraction of a second. In your case, and in the case of the RX450h, it seemed longer. And scarier.

TOM: So while Toyota might be right that the ABS is working the way it was designed to work, it offers the driver less confidence than ABS systems in other cars. And for that reason, we think a fix is called for.

RAY: My own guess -- and I want to emphasize that this is pure speculation -- is that it has something to do with when the hybrid switches from regenerative braking to traditional friction braking. And that if the ABS deploys (even properly) during that moment of switchover, it creates a strange delay. I would think it's the kind of thing that likely can be fixed with software, but perhaps it's not that easy.

TOM: Interestingly, Toyota has recalled the newer Priuses (the 2010s) to fix what sounds like a very similar problem. Here's Toyota's description of the reason for recalling the 2010s:

"Toyota has received complaints of inconsistent brake feel during slow and steady application of brakes on rough or slick road surfaces when the anti-lock brake system (ABS) is activated in an effort to maintain tire traction.

"The system, in normal operation, engages and disengages rapidly (many times per second) as the control system senses and reacts to tire slippage. If the same brake pedal force is applied under these conditions, in the worst case, this may lead to an increase of vehicle stopping distance and thus raise the possibility of a crash."

RAY: They say that the older Priuses, like yours, use a different ABS system, and so are not subject to this recall. But it sounds like a similar issue. So we have to wonder if the recall eventually will be expanded to include older Priuses, too.

TOM: In the meantime, here's what you can do to help. Go to www.safercar.gov, which is the website of NHTSA, the National Highway Traffic Safety Administration. It collects reports of safety-related concerns. And if there are enough verifiable complaints, NHTSA can launch an investigation that may lead to a forced recall.

RAY: But before it ever gets to that, we hope that Toyota will learn from the mistakes of GM and, more recently, Toyota, and step up and offer a fix. If for no other reason than that customers like you, Betsy, are lacking confidence in their cars.
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