luder888

I've always been apprehensive about using ACC in traffic because I don't know if my brake light will constantly be flashing on and off like an old lady driving in order to maintain a constant speed.

Well tonight I went for a test drive, set my cruise to 80. As it approached a car going about 70 the car slowed down gradually but the brake light didn't come on. However, if it had to slow down more then the brake light did come on. I think there is some tolerance built in that even if ACC has to apply the brake, if the pressure is light then the brake light doesn't come on. However, if it's over a certain threshold then it'll activate the brake light. I like this feature because it mimics more like real-life driving and reduces the amount of time the brake light gets activated. I'm still trying to learn the little things Audi put into their cars to make it great.

I used painter's tape and taped a piece of foil onto the LED brake light running down to the rear window so I could see the brake light reflection. Now if someone knows of another way to see if the brake light is on when driving (i.e. via the ODBII dongle) I'd like to know!

machz

Thanks for the test I was wondering the same thing myself. I hated the thought of the brake lights coming on everytime the car had to slow slightly.

Nikon1

heisnuts

Our cars have regenerating braking to help keep the battery charged and help reduce the load on the alternator a little bit. I wouldn't be surprised if the car is using the regenerative braking under light braking and that is why the brake lights did not come on, and once actual braking was needed that is when the the lights turned on. I know when using traffic jam assist when the car is at a stop in traffic the brake lights are on until the car starts to move again.

luder888

Maybe one of these stuck on the rear hatch glass will allow me to see the brake light and do another test:

Can't leave that on permanently though since it's butt ugly. Does a cheap ODBII scanner allow you to see real-time brake light status?

Slides

It does? Source?

superswiss

When ACC needs to slow down it doesn't necessarily use the brakes to do so. Depending on your Audi Drive Select mode and the distance setting and how rapid the car in front slows down, it may simply just let off the throttle and use engine braking to slow down. In Comfort mode with proper distance setting and somewhat even flowing traffic it may never apply the brakes and just let off the throttle to slow down. In Auto and especially Dynamic and if you set the distance to the shortest setting than it will naturally use the brakes more as there is less room and you asked it to operate more aggressively.

As for the regenerative braking, I believe that is now standard in all models, but not a 100% sure. However, the way it works is that during coasting and braking the alternator voltage is increased to charge the battery faster and then later the alternator can be decoupled temporarily and the car can draw the energy required back from the battery. This system has been in use by Audi for a while. It's even in my 2013 RS5. Not sure about a good source where it's being explained, but it has been mentioned in the press in the past. I don't remember where I first read about it.

heisnuts

2018 Audi A5 Tech Specs | Audi USA

look just under the auto start/stop feature.

Slides

Speaking of ACC, I haven't been able to fully trust Traffic jam assist yet. So far, I always instinctively press the brakes to stop the car even my car seems to be doing it on its own. Just can't mentally trust it. It's an odd feeling.

Any tips on best settings for Traffic jam assist?

superswiss

Not sure there are best settings. I keep the distance setting in any car with ACC set to the shortest most of the time. That gives the smallest gap and the least likely scenario of somebody cutting in, although it still happens. You'll have to get yourself to trust it, otherwise no setting will make a difference. It's definitely an odd feeling at first. I don't remember how long it took me, but I was a bit on the edge at first. After a while I learned how it reacted and I started to trust it. Now after 5+ years my trust issues are all gone and I instinctively know when I need to manually intervene, often before it even alerts me. It has become a symbiosis between man and machine sort of at this point.