Puzz1

When using adaptive cruise control, does anyone know if the rear brake lights activate when the car slows itself on the highway when approaching a slower vehicle? I never considered it until my wife asked the other day.

CanAm Eight

It’s my understanding the brake lights only activate when the cruise control calls on the vehicles brakes to slow down.

Interesting if someone has seen documentation on this.

AudioBear

I was recently in a caravan with 3 Audi A6s including my own. We were all set on adaptive cruise. The brake lights came on when the front car's brakes came on and sometimes momentarily when he turned off cruise to decelerate slowly. If he used the brakes the cruise did. From this I concluded it does what it needs to do to slow down and if it uses the brakes the lights come on. By doing it this way the car behaves just like a car without adaptive cruise. That's how it seemed to us anyway.

Jack88

I don't see why they wouldn't activate the brake lights when the brakes are being used. It would be violating some kind of law.

snagitseven

Braking shouldn't occur when the ACC is turned off. By definition, the ACC is completely disengaged so it's auto braking feature can't occur. The only exception where this could happen with ACC turned off would be if the Presense front Brake Guard was activated and the car was about to collide with a followed car.

RED HORSE

While traveling in nearly stop and go traffic one night I had the same question, and yes, I could see the reflection of my brake lights as they came on when the car was slowing down to keep from hitting the car in front. I presume this is that case no matter what speed you are going.

snagitseven

Well, yes and no. It would depend on the distance setting on the ACC stalk, the setting in the MMI (Dynamic, Auto or Comfort) and the rate of slowing of the car in front. The ACC might not have to engage the brakes to slow down; releasing of the accelerator to coast might be enough to keep the car in an acceptable distance range. If the car in front comes to a stop, obviously the brakes will always engage.

Puzz1

Ok, thanks for the replies. I was concerned that a car approaching from the rear wouldn't notice the ACC slowing the car down vs pitting the brakes manually.