Cruise control and DSC, do brake lights go on when these are engaged?

arleitiss · 08-05-2014 12:49AM #1

Hey, just out of curiosity -
When Cruise control is on, lets say set at 100 km/h, and you go downhill on motorway or if you press button to reduce speed - do brake lights come on? I mean I can imagine it looking weird - flickering every second or so?

Same with dynamic stability control/traction control - when one of the wheels loses grip it applies brakes to some specific other one - would lights come on?

Asking because just out of curiosity

not something I could test by myself really nor I would.

drunkmonkey · 08-05-2014 12:54AM

I kinda wondered the same thing, sometimes I slow down using the cruise control and wonder do the brake lights come on but I assumed it works like a truck and it's actually breaking using the engine rather than the brakes so no brake light comes on.

Frynge · 08-05-2014 12:56AM

When I'm driving it is mostly on cruise control and the brake lights do come on when the car is going down hill and it's speed increasing. But it can go quite a few mph above what it is set too before it kicks in.

keithclancy · 08-05-2014 07:38AM

arleitiss wrote: »

Hey, just out of curiosity -
When Cruise control is on, lets say set at 100 km/h, and you go downhill on motorway or if you press button to reduce speed - do brake lights come on? I mean I can imagine it looking weird - flickering every second or so?

Same with dynamic stability control/traction control - when one of the wheels loses grip it applies brakes to some specific other one - would lights come on?

Asking because just out of curiosity not something I could test by myself really nor I would.

Cruise Control doesn't use the brakes to slow you down, mere disengages the throttle.

Traction control does not engage your brake lights

cml387 · 08-05-2014 08:15AM

Cars have become very sophisticated in terms of software etc., but the brake light is still activated by a switch on the brake pedal. So no, slowing down by using cc won't activate the brake light. Anyway the reduction in speed is no more than if you took your foot off the accelerator.

CiniO · 08-05-2014 09:03AM

arleitiss wrote: »

Hey, just out of curiosity -
When Cruise control is on, lets say set at 100 km/h, and you go downhill on motorway or if you press button to reduce speed - do brake lights come on? I mean I can imagine it looking weird - flickering every second or so?

No, they don't because you are not braking. All your car can do is to slow down by applying no throttle.

Same with dynamic stabileity control/traction control - when one of the wheels loses grip it applies brakes to some specific other one - would lights come on?

Asking because just out of curiosity not something I could test by myself really nor I would.

Impossible what you described. If only one wheel loose grip, it means it's spinning and brake is applied to this particilar wheel - no other.
No brake light in this case anyway because car is not even slowing down.
In case of 2 (or more) wheel skid, stability controll will indeed choose appropriate wheels to brake to recover, and I don't know if light will come on or not. Possibly depending on car they could as this usually slows down the car a good bit

_Kaiser_ · 08-05-2014 09:36AM

I used to use CC a lot in the Passat, but I've found myself using it less since I changed.. partly because until you get beyond the Dublin county limits there's not much point but also because it feels like it uses more fuel than just using the throttle manually - eg: if going downhill on a motorway you can just lift off whereas with CC on it still seems to be pulling.

All in my head or am I right?

boardzz · 08-05-2014 09:38AM

Pretty sure the brakes are applied for adaptive cruise control which will engage the brake lights.
Normal cruise control just lets the car slow down.

No Pants · 08-05-2014 09:58AM

Kaiser2000 wrote: »

I used to use CC a lot in the Passat, but I've found myself using it less since I changed.. partly because until you get beyond the Dublin county limits there's not much point but also because it feels like it uses more fuel than just using the throttle manually - eg: if going downhill on a motorway you can just lift off whereas with CC on it still seems to be pulling.

All in my head or am I right?

For the most part, I only use cruise control on motorways. Any other roads, unless especially clear, can be quite frustrating otherwise.

My thinking is that cruise control would keep your fuel use rather stable, as you're not opening and closing the throttle. However, to prove it either way would need testing; using CC and monitoring mpg over a period, maybe a week, and then monitoring it over a similar period, but not using CC. That's assuming your weekly mileage is fairly static. I suspect you drive more miles than me.

pred racer · 08-05-2014 10:13AM

Kaiser2000 wrote: »

I used to use CC a lot in the Passat, but I've found myself using it less since I changed.. partly because until you get beyond the Dublin county limits there's not much point but also because it feels like it uses more fuel than just using the throttle manually - eg: if going downhill on a motorway you can just lift off whereas with CC on it still seems to be pulling.

All in my head or am I right?

My cruise control is more frugal than me!

tossy · 08-05-2014 10:18AM

pred racer wrote: »

My cruise control is more frugal than me!

Ditto, the only way i see economy is with CC on, it also definitely doesn't use the brakes. I found different cruise control systems vary when it comes to keeping speed in check on downhill runs, my Bora was good, the A4 wasn't so good and the S3 is as good as the Bora was.

drunkmonkey · 08-05-2014 10:26AM

When I slow down using the cc lever it slows very quickly, more than if I just let my foot off the accelerator so I don't believe it's just cutting the throttle there is some breaking going on but I think it's the engine.

jimgoose · 08-05-2014 10:28AM

The cruise-control on my 1999 S-Type does indeed apply the service brake gently when needed. No brake-lights though, as pointed out that's brake pedal switch only. It'll only do that in situations like when the road gradient changes fairly quickly, and the actual brake is needed to modulate speed. You'll also feel it braking gently now-and-then on a prolonged, pronounced gradient.

Cruise control is certainly more frugal than I am. The computer knows each second precisely what amount of throttle is needed to maintain a given speed. Also, when acceleration is needed - like when hitting "Resume" after scrubbing off a good bit of speed for whatever reason - it focking floors it Fintan, which is the most efficient way with modern EFI setups. If you want it to shift, give it the boot. If you don't, don't. :cool:

BobbyBingo · 08-05-2014 10:32AM

Cruise control (non-adaptive) on my car does (defo) activate brake lights on slowing down. Not sure about the DSC though never thought about that before..

B

Mc Love · 08-05-2014 10:39AM

The very question thats been bugging me, is it better to use cruise control in terms of saving fuel or not? I know it might save you on speed fines alright

CiniO · 08-05-2014 12:05PM

No Pants wrote: »

My thinking is that cruise control would keep your fuel use rather stable, as you're not opening and closing the throttle.

You are not opening and closing the throttle, but your cruise control is.
When activated, goal of cruise control is to maintain set speed, so this needs permanent adjustment of throttle to accommodate for inclines and declines in terrain.
Cruise control is not meat to be be economical. It's just to maintain set speed.
If you want to save fuel, don't use cruise control.

CiniO · 08-05-2014 12:06PM

BobbyBingo wrote: »

Cruise control (non-adaptive) on my car does (defo) activate brake lights on slowing down. Not sure about the DSC though never thought about that before..

B

What do you mean by "slowing down".
Cruise control is to maintain set speed.
You can cancel it, then car slows down.
You can also lower the speed with the buttons.
But I don't believe any car would turn on brake light for such subtle speed adjustments. Would be silly IMO.

whomitconcerns · 08-05-2014 12:18PM

if i drop the cruise control from 129kph to 105kph there is a definite breaking effect and not just engine breaking or lack of throttle. If you hold the switch on the audi it changes cc speed by 10kph per "hold"..but I dont know about break lights..and its not something I would re do..I imagine its stressful on whatever the car is using to slow down, esp if not the brakes.

keithclancy · 08-05-2014 01:37PM

whomitconcerns wrote: »

if i drop the cruise control from 129kph to 105kph there is a definite breaking effect and not just engine breaking or lack of throttle. If you hold the switch on the audi it changes cc speed by 10kph per "hold"..but I dont know about break lights..and its not something I would re do..I imagine its stressful on whatever the car is using to slow down, esp if not the brakes.

Yeh, Audi Adaptive Cruise control.

Never liked it, pretty wasteful on fuel imo.

kirving · 08-05-2014 02:17PM

I know that the manual for my car, it states that the indicators and brake lights will flash if the ABS is activated, or if the deceleration exceeds a certain amount. I'd imagine that the lights will go mental if the DSC recognises a big spin or complete loss of control.

BobbyBingo · 08-05-2014 02:22PM

CiniO wrote: »

What do you mean by "slowing down".
Cruise control is to maintain set speed.
You can cancel it, then car slows down.
You can also lower the speed with the buttons.
But I don't believe any car would turn on brake light for such subtle speed adjustments. Would be silly IMO.

Sorry - what I mean is : say I'm set at 100 and hit the top of a hill - on the downhill as the car gains speed the brake lights come on to reduce speed back to 100. It's quite possible, although I don't know for sure, that the brakes are applied only after it closes the throttle and discovers it's not losing speed, if you know what I mean ?

B

BarryD · 08-05-2014 02:43PM

CiniO wrote: »

Cruise control is not meat to be be economical. It's just to maintain set speed. If you want to save fuel, don't use cruise control.

That's my experience, if you drive with normal foot control on throttle, I think you tend to naturally slow down a bit on uphill stretches and then pick up again. Cruise control just powers you up the hilly bits at a constant speed and uses more fuel as far as I can see.

Then there's the separate safety issue - it's so easy to be a bit slow knocking it off coming up to a bend or other traffic on main roads other than motorways. Whereas your foot has automatically eased off if driving with CC.

BarryD · 08-05-2014 03:27PM

BobbyBingo wrote: »

Sorry - what I mean is : say I'm set at 100 and hit the top of a hill - on the downhill as the car gains speed the brake lights come on to reduce speed back to 100.

Ours VW, doesn't slow down going down a hill when in CC - it just speeds up as far as I can see. You have to actively brake to keep within speed limit.

Come to think, cars back in the 1970-80s etc. were much better when going down a hill. There was no power steering etc. So you could turn off the engine and just cruise down, free mileage of sorts

Used to be able to get from Wicklow Gap all way down to junction with Glendalough without a drop of petrol. Probably illegal, even then, but very green

CiniO · 08-05-2014 03:57PM

BarryD wrote: »

That's my experience, if you drive with normal foot control on throttle, I think you tend to naturally slow down a bit on uphill stretches and then pick up again. Cruise control just powers you up the hilly bits at a constant speed and uses more fuel as far as I can see.

Then there's the separate safety issue - it's so easy to be a bit slow knocking it off coming up to a bend or other traffic on main roads other than motorways. Whereas your foot has automatically eased off if driving with CC.

Exactly as you say.
Cruise control is pretty much only handy on longer motorway travels in low traffic, hardly any other circumstances.
But then - once you are travelling longer distance on motorway in low traffic then it's absolutely brilliant.
I'm driving between Ireland and Poland once or twice a year every year, and getting a car with cruise control made an horrendous difference in that journey. It's so much more nice to drive with it.
I especially love going through Germany at night with nearly zero traffic when you can set your cruise control at 200km/h and keep going for 2 hours without really any need to slow down

ShanE90 · 08-05-2014 05:31PM

Cruise control "with brake function" is fitted to 6 cyl BMWs it will apply the brakes when you exceed the preset limit and if you pull the stalk towards you full braking or near enough full braking power will be applied and the brake lights activated

Cruise control and DSC, do brake lights go on when these are engaged?

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