New to the Lexus family, and went on my longest drive in new RX350 yesterday and noticed an odd feeling from car suspension/drivetrain when going down a roughly 8% grade with Dynamic Cruise control on 60mph. About a 1/4 mile into the downhill of about 2.5 miles, I noticed an odd bouncing/vibration sensation coming from the car - almost felt like a tire quite a bit out of balance or soft tires in very cold weather that had flat spotted. The car rides perfectly smooth at all other times, and the pavement on that section of road is relatively new and not wash-boarded. As soon as I got to the bottom of the grade, the ride smoothed back out to normal. Being new to a Lexus, the only thing I can think of is maybe the car pulses the brakes a bit on cruise when it senses a longer downhill grade versus downshifting the transmission - I just don't know the answer to that one. My Q5 would use the brakes in a near constant and linear way on this same stretch when in cruise control, but would downshift if cruise was not on. Either way, this was an odd experience and didn't feel quite normal, so seeing if anyone else has noticed this or knows how the dynamic cruise system works when on steeper downhill grades. Thanks in advance...

 

Assuming you haven't turned off the brake light indicator on the bottom of the gauge display, look there next time to see if it is pulsing them.

 

Didn't think of that - good idea. I'm an electrical engineer by trade and have been trying to find technical information on how the systems function, but most of it is proprietary IP, so I can only get so far. Thanks!

 

I don't feel the vibration but mine does rev up the engine on a steep down hill up to 4000 for several seconds which I am assuming is doing engine braking and perhaps regeneration. Anyone else noticed this rev up to 4000?

 

Same, I thought it had some kind of brake assist as I was going down a mountain road, dealer said it was regeneration. Cheers.

 

Exact same thing happened to our 2018 RX while on a long distance downhill drive with the dynamic cruise on. The steering wheel shuddered and immediately I knew the brakes had overheated and warped the discs. It drove fine on level ground and braked OK. Took the vehicle in to the dealer for a brake inspection. Technician came back and confirmed my suspicion. All 4 brakes overheated and warped the discs. My vehicle only had 11,000 miles. Service advisor said all brakes had to be completely overhauled. Since the vehicle had so low miles plus it wasn't my fault, the complete brake job was free. After the repair, I quit using cruise when going downhill.

 

That's good info to have @YWW; we had this happen again twice this past weekend - once on the same stretch of highway as before and yesterday on a different but similar grade roadway. Yesterday's occurrence was bad enough that my passengers even commented on it, and the driver behind me got really ticked off and passed us as soon as he could. This time the issue was more pronounced than before - the car would automatically brake every 3-4 seconds for about a half second at a time, over and over and over. We were at a steady speed of about 58 mph, no cars in front of us, and no guardrails or jersey-barriers that might have triggered the front or side radar sensors. It does seem that this is some sort of calibration issue, and the braking stopped as soon as I turned off the adaptive cruise. Main concern this time was that the car behind us almost hit us for that 20-30 seconds that the Lexus started doing this and before I could get the system turned off. Very unnerving... I'll be having the system and sensors checked soon, but not using this feature on steep terrain again unless Lexus finds something definitive that is causing it.

 

How do you turn off the brake light indicator ?