Driving today in my 5 day old Gen 3 Prius and had a worrying experience.

Heading down a slight hill and applying light braking, when the car suddenly seemed to have a surge in power and accceration. I had to brake hard otherwise I would have been into the back of the car in front.

Everything seemed to go back to normal, and I travelled the remaining 20 miles of my journey without any problems.

However just after this incident occurred, my wife in the pasenger seat asked if I had turned the air con off as it was getting warm in the car. The air con was still switched on but even turning down to the coolest setting still produce any cold air.

So it looks like the air con has packed up, but whether on not the two problems are related remains to be seen.

Called my dealer when I got home, but can't get in until next Tuesday. I told the service dept I can manage without a/c for a few days, but am obviously very concerned about the power surge problem, but they still won't look at it until Tuesday.

Guess i'll have to drive carefully over the next few days!

There have been a number of threads on Priuschat about the surge or acceleration under light braking when the front wheels hit an uneven, rough patch of road. I haven't had time to follow much of the Gen 3 info.

The explanation (from the technically minded Gen 2 owners) goes that under light braking, almost all the braking is regenerative using one of the Motor/Generators, if you hit a bump, the traction control detects a loss of traction and switches over to friction braking, during that fraction of a second when it is switching there is no braking as the regenerative braking has been switched off.

Although I've experienced some odd braking in the Gen 2, I wouldn't myself be so sure that there isn't a problem with Gen 3 especially as it a new model.

Thanks for the info. There are some interesting posts on the Prius chat forum about the 'problem'. At least I can be sure now that I didn't imagine it.

There seems to be two opinions on this:

Either its 'just the way the braking is designed to work', or 'its a potentially serious problem which toyota need to sort out'

I know it scared me when it happened. I'll mention this to the service guys next week, but as someone on Prius chat says, they will probably drive it round the block and say everything is ok.

Some posts on Prius chat suggest the 'problem' also exists on gen2 models.

I had a vague recollection of it happening before and trawled back through the forum and found this entry which I posted in Sep 2004. http://toyotaownersclub.com/forums/index.php?showtopic=23062

Took the car in for the air con check today and was advised that it was functioning correctly. However it was quite warm outside when I collected it and so I gave it a try again. Pressed the auto button and set the temp to LO, but still blowing warm air.

Then it hit me. The a/c light was off, so the fans were blowing in air, but not cooling it. Pressed the a/c button and managed to get cold air at last. After a few tests I realised that the a/c button has to be on all the time. This may seem obvious, but I'm sure in all the cars I had before with auto a/c, simply hitting the auto button and setting the temperature is enough to control the temp, automatically switching on, fans and a/c as required to naintain the set temperature.

Checking the manual, page 281, says "Press auto and the a/c will begin to operate, then adjust the temperature"
However page 287 contradicts this and says "a/c does not operate even if it pushes auto".

Seems a bit odd having an auto button if it isn't capable of automatically controlling the temperature.

I also asked if the indicator volume could be increased as it's barely audible particularly when the audio is on. But they advised me that it was set correctly and can't be increased.

Lol, this caught out the salesman on my test drive also. Baking hot day, car not cooling down as he explains how climate control works, fan speeding up etc. Car stayed resolutely hot until I prodded the A/C button. Indeed in all other cars I've had, like you, A/C is inherently on and available, and the temp just uses it as needed.

The only thing I can think of is that its to try and encourage energy saving, by requiring you to turn on the A/C when needed as opposed to it being on when not.

Interestingly when part ex-ing my last car the salesman was very particular as to whether it had A/C or Climate control. No idea as to what I'd say for the prius.




Doesn't surprise me...

Brochure says "Dual Zone climate control air conditioning".
The Toyota website configuration says "Auto air conditioning".
And the spec section of the same website "Air conditioning system - climate control"

So even Toyota don't seem to know whether it's dual-zone or single, air con, or climate control.

Hi there, for the record I had a similar experience in my 1-day old Gen 3 Prius last week.

Also heading downhill, braking lightly from about 40 mph approaching a roundabout, when the braking seemed to momentarily disappear. I wouldn't say the car accelerated but as I was anticipating the deceleration (and the car was heading downhill) there was a sensation of jumping forward. I didn't have any cars immediately in front but also braked hard as the roundabout was suddenly a lot closer than I'd anticipated - it was enough to set my heart racing!

I don't think there were any potholes or drains to cause a loss of traction (although it was raining) but given the conditions it could fit with the idea that the car was swapping from motor braking to conventional braking at the time. Then again I would have expected a seamless transition for such a critical function.
I think I was using the a/c to keep the windows clear although I'm not convinced changes in demand from the a/c would affect braking (which is presumably controlled by the electric motor and the conventional brakes?).

Regards
DrCez

P.S. I've only had this experience once although I haven't done a lot of mileage to date.