RXSF

Last year there was a recall for the Prius because the regen brakes would switch to regular brakes specifically during bumpy roads/pot holes causes a 'surge' in vehicle speed because of the non linear feeling of the braking.

Well, Ive noticed that my RX does the same in that it also switches to regular brakes always while braking on a road with a lot of bumps. This causes the car to brake less than it would have if it stayed in regen, and vehicle speed is not reduced at the same level. Just curious if perhaps the Prius brakes was a more severe version, or perhaps this is common to the hybrid powertrain, or perhaps this is an oversight in that a recall should be placed for all Lexus/toyota hybrids. I still havent quite gotten used to the two difference braking modes. There is definitely a 'surge' as it switches.

sleepysurf

The "relative surge" when the regen brakes switch to anti-lock brakiing on a bumpy road has been discussed a fair bit on this board. However, I don't recall (pun intended) hearing about any Prius recall for that particular issue. Do you have any links?

RXSF

http://abcnews.go.com/Blotter/toyota...ory?id=9719905

sleepysurf

It's pretty clear this is NOT any kind of mechanical/electrical problem, but just the well-recognized transition from regenerative to anti-lock brakes. The ONLY way a driver could "accidentally" hit a car (or their house!) in front of them is if they panic and release the brake. I've experienced this exact issue many times when braking on a bumpy road (or going over railroad tracks/potholes), and as long as you keep firm pressure on the brake pedal, it functions exactly as it should, albeit with a momentary "surge" then "pulsation" as the anti-lock brakes kick in. Will be interesting to see how long before the American public and lawyers likewise start crying "wolf".

DunWkg

I'm not that sensitive to changes to notice transition from regen to ABS or call it a surge. Lunge comes to mind. I have been fearful of hitting the car in front of me many times as suddenly I feel I'm in free flight headed toward someone's bumper. I've changed my following habits to increase the distance from the car in front of me. Probably a good thing anyway!!

I really don't like that transition, surge, or lunge feeling. Disconcerting.

RXSF

its weird that they would program the brakes to switch while going through bumpy roads. I wonder what the logic is.

HiYee

I also experience the same problem with my 2010 RX450h. My car was travelling at normal city speed 50km/hr. I put my foot on the brake paddle lightly to slow down. The car was fine until one of the wheel hit an uneven road surface, like a utility cover on the pavement, the car 'surge' ahead for a split second. This is a kind of scary feeling because you are expecting the car to slow down instead of speeding up.

From the previous postings, looks like I am not the only one who get this brake problem. I am wondering if there is a fix or software patch from Lexus to resolve the sudden surge problem. For a car this expensive, this glitch should not have happened. I have been driving my 2008 Prius for 3 years, I don't experience something like this. It is quite a disappointment to see that a RX hybrid is not as good as a Prius.

sleepysurf

Here's the explanation from Toyota regarding the same issue with 2010 Prius models... http://www.autoobserver.com/2010/02/...n-braking.html

Looks like Toyota DID implement a software fix to reduce the time lag in switching from regenerative to antilock brakes, but (apparently thus far) is not offering it for older Prius (or RX 450h) models.

As I mentioned in previous posts, when this momentary "surge" occurs, you need to continue to press firmly on the brake pedal. I think the issue is that this relative "surge" surprises drivers experiencing it for the first time, and their initial response is to momentarily ease off the brake pedal, which further exaggerates the effect. It happens to me a fair bit, but I'm totally used to it, and it hasn't posed a safety issue. I do see how it theoretically could, if you were following another car very closely, and had to panic stop on a bumpy surface.

If Toyota/Lexus has indeed upgraded the brake control software, they should issue a TSB (if not a full recall) to deal with it. I guess they don't really want to admit yet another engineering "flaw" in the midst of so many others lately.

RXSF

I have come to just accept it. I dont think the vehicle surges, it certainly is not accelerating. It is simply not braking to the same degree. Because I like to use the regen brakes instead of my brake pads, I usually release the brake pedal and then press it again to reactivate the regen braking system

billy44bo

" I usually release the brake pedal and then press it again to reactivate the regen braking system" Why not press down harder on the pedal and see what happens and not lose the the time and whatever braking power you do have?

RXSF

my reasoning is that Id rather use the regenerative system to brake rather than the brake pads

obviously I do it when I still have a large space in front of me to brake

DunWkg

I'm usually in a split second panic and press harder. My foot too slow to push, release, push again while bouncing over a pot hole headed towards someone's rear bumper.

kitlz

I feel it too but have adjusted. Only once did I feel scared. Damn roads are horrible around me which doesn't help.

HiYee

sleepysurf, thanks for the information. I guess I have to just get used to it. The only challenge is that it won't happen when I am expecting it, and it will happen when I am not expecting it.