I've had my SH-AWD TLX Advance for about 3 weeks now. I'm really, REALLY appreciating the change from my 2010 RL.


An oddity - has happened twice - so not declaring it a problem...


I regularly encounter a couple of steep downhill stretches with 45-50mph speed limits. Nature of traffic is that I often use cruise control. The RL would let me get 5-6 mph above set speed before dropping down gears to reduce speed. The two times I've waited for the TLX to drop down, the transmission has done 'something' but speed jumped to 10+ over so I've braked manually (and quickly). I'm not sure if the transmission was in neutral determining which gear to downshift to or what.


Any one else have any experience with ACC in this scenario??


Next opportunity I will set speed at 35 and see if I get it to downshift...

 

Adaptive Cruise Control is different to the industry Dynamic Cruise Control, where the latter till hold a set speed in any condition. Not sure if the RL had ACC or DCR. ACC manages the speed based on a detect vehicle ahead, and if there is no vehicle then it will not drop below the set speed, but will exceed the speed. This mean the car is free to go faster on a decline.

I think, but don't quote me, that there is some learning process with the ECU that may moderate the speed some time after learning your habits. Unfortunately, there are no roads like yours in my driving range so this is pure speculation.

 

This situation was exactly explained in the video posted today in the 5th Gen TLX-specific forum on the "TLX 9spd Transmission Concerns" thread.

https://acurazine.com/forums/fifth-g...ncerns-929652/


At around 17:45 it talks about dog clutch operation removing engine braking momentarily when downshifting to reduce speed...I linked to the thread - wasn't sure how to insert the actual video...

 

Ouch, that's scary. I've had my car normally seem to slow down using a type of braking to maintain speed, but I've never had it accelerate.

 

On this one particular downhill my 2010 RL might hit 7-9 mph over the set speed before downshifting to a low enough gear to reduce speed. The speed limit is 40 mph, last week in my TLX I set the speed at 35 mph but it went through a couple of gears - each time taking a moment in neutral where speed accelerated - I applied brakes when I hit 50 mph. I was surprised it was +15 over the set speed and still hadn't gotten into a gear to reduce speed...