Cartoon

Question or inquire, while descending down a extended long steep grade at a speed of 75 mph , after about 15 min or so their is a excessive vibration like sitting in a vibrating chair, ( no brakes applied just costing ) and as soon as you give it throttle it stops but back off the throttle it starts. I now its the wheel motor as it go's into charge mode but is this normal, it will not do it on small grades just extended extra long steep grades highway speed ?? 2014 RX450H 22000 miles

User 41924

I'm pretty sure that's not normal, and I would have it checked. Our 2013 goes into what I think of as the engine braking mode most often as we're coming down out of the mountains. I can hear the ICE as it starts to spool up, but there is no vibration associated with it at all. Same with my CT.

Cartoon

Try to contact Lexus Canada but they have no Teck support for the public. No sense taking it to the dealer as there is no steep hills around to duplicate the problem. I have spoken with a service manager and have not heard back yet??

Droid13

Yea, it definitely would be a challenge I think to diagnose that particular problem for the mechanic. My guess is after a while descending a hill, you will reach a certain point where the regenerative braking is cancelled. During normal driving the traction battery is never fully charged to leave a bit of room for regen braking, but on a long descent you will reach a point of maximum allowable charge and the regen will cease. At this point, you'll just have the engine spinning with no resistive load from the motor and maybe you've got some perfect spin combination resulting in resonance in or near the PSD (aka CVT). As a suggestion, try using the "S" gear positions to alter mechanical speeds inside the PSD. It's probably not a bad idea to drop down a notch or two anyway in long descents.

Cartoon

I have looked into this a bit more and came across a interesting read ...........https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive