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Regenerative Braking Issue


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Hi all,

I'd really like some views on how my RX400h is behaving, if possible. I've been driving it for about 9 months now, so have tuned in to the way the hybrid drive works, and what it is supposed to do when. However, I think there is an issue with the regenerative braking. To me, it seems that normal behaviour is that when performing ordinary braking manoeuvres, the electric motors are engaged in "generator mode" to help slow the car down and harvest the kinetic energy - the power meter dips into the blue section to show that this is happening. On my car, this mostly works, but also frequently seems to "drop out" during a braking manoeuvre - especially then travelling down hill. I can feel the braking effectiveness suddenly reduce (it feels almost like the car has hit a patch of black ice), and the power meter rises back up to the zero position.

I mentioned this to my dealer when the car was serviced a couple of weeks ago, and they checked for fault codes (none), and "reset the hybrid drive", whatever that might mean. It did seem to resolve the problem for about a week, but now it is back to its old ways. As an illustration, we took the car to the Alps a couple of months back, and on a daily basis we drove down hill at the end of the day back to our apartment - hundreds of metres of descent probably taking 10 mins. There seemed to be little regenerative braking after an initial period, and we never got the energy bars all lit up, all week.

Has anyone experienced anything similar? Any advice? The car is still in warranty for about 3 months, so I'd really like to get it sorted if there is a problem to be resolved. Any advice on what to say to the dealer?

Thanks in advance ... Nick.

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  • 2 weeks later...

  • 4 weeks later...

it's very difficult to get the bars fully to the top. I achieved it in winter mainly because the temp was so low the engine seems to be on all the time.

The regen stops for a couple of reasons, 1 - if the batteries are full which is not very often, or 2 - more commonly, the hybrid system/battery temperature is too high so only a very limited amount of charge is put back into the batteries. This happens quite often on my vehicle but rarely does it happen during breaking and normally it is progressive, i.e. you see the power meter slowly come up.

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Thanks for your reply Colin. It's definitely not reason 1, but reason 2 is intriguing, i.e. it might be to do with temperature somehow? However, as per my original post, the most obvious manifestation was on an alpine mountain road, and in the ski season, so over-heating very unlikely. Gives me something to prompt the dealer with though, as they came back with "seems fine to us" last week which was frustrating.

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if the hybrid system is in a lot of use, e.g. a lot of acceleration/deceleration then charge is being drawn from the batteries and recharged via engine and regen then the batteries will get very hot and the system will limit the recharging current and also the amount of electric assistance, ambient temperature won't affect things too much. One question to ask, were the air vents below the rear seats obstructed? That would make Battery temps even worse.

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Fantastic - good thought. The dealer guys have agreed to come to my house (30 mins drive for them) so I can take them to places where I know it happens - I'm impressed with their dedication! Will feed that thought in and report back ...

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My car is also like this and caused me an incident when i first picked it up prompting me to take it back to lexus. After a lot of deliberation. They told me the car was fine. But it has exactly the same symptoms so would be really interested in how you get on. PM me if neccessary

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  • 2 weeks later...

what age are these vehicles?

I would like to think newer ones have updated software which has been improved over time. Unfortunately Lexus dealer in the UK don't seem to provide software updates, even when I've asked. Mercedes dealers seem to upgrade software automatically as part of a service and even Lexus US dealer will perform updates if asked.

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Fantastic - good thought. The dealer guys have agreed to come to my house (30 mins drive for them) so I can take them to places where I know it happens - I'm impressed with their dedication! Will feed that thought in and report back ...

That was more thn two weeks ago, do you plan to report?

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  • 2 months later...

I've just noticed my 2010 rx450 do the same a few times today for the first time. No discernible change in weather conditions or anything else obvious unless it is a reaction to being pressure washed etc? Very strange feeling though.

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I have had my 06 RX400 for about six weeks and have noticed the change in braking when going down hill it actually feels as if the ABS is kicking in but without the judder. I have not reported this as yet as I have no problem controlling it with extra pressure on the brake.

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