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I had this happen before at a low speed, but this one was at high speed.
I was on ACC on highway travelling 65 to 70 mph. I could see on Navtraffic that we were approaching a slow area. Cars in front started to brake and I was expecting ACC to kick in and slow car. Suddenly I see that slowed traffic is actually stopped. In very quick succession, the collision avoidance lights up, but no braking applied. I hit the brakes and see that we are probably not going to stop in time. I steer to side lane (no one right beside me) and stop barely in time of car that was directly in front of me. I was braking hard, but not completely all out on the brakes.
Sure expected ACC to start slowing us down before I had to manually apply brakes.
Wow, getakey. Never mind the ACC, the CMBS should have come on and tightened your seatbelt and applied the brakes. Had you disabled the CMBS? I think that ACC and CMBS must use the same forward facing radar, so perhaps the whole system failed. I would definitely have your dealer check out the radar. Though if ACC was keeping you at a set distance, that radar would seem to have been working. Perhaps someone else (looking at you, pgeorg) can confirm that ACC and CMBS use the same radar.
Of the top of my head i believe the CMBS does use the forward facing millimeter wave radar, and i also believe the CMBS is controlled by the ACC unit. Let me look it up, and i will post what i find in a few.
You are correct fsmith, the CMBS and the ACC use the same radar. Also the ACC unit controls the CMBS......
Below are a few details of how the CMBS works, and pay particular attention to the first image:
I would definitely make an appointment with the service department right away, especially if you use the ACC frequently.
to be clear, the 1st stage Collision avoidance engaged - I got the MID, but brakes did not engage. That said, I was quick to hit the brakes when the alarm activated, so maybe it was beginning to apply braking, but I over-rode it with my own braking.
I would have expected ACC to engage brakes based on distance prior to 1st stage Collision warning. I was kind of waiting for ACC to slow and did not really notice that cars were actually stopped until the alarm came on. Then realized we were closing very fast.
I believe at this point the seatbelts did tighten, but I was too focused on the braking and if I had to swerve.
My biggest concern was why ACC did not slow down before Collision avoidance was activated in stage 1.
This was on a perfectly straight section of road, car in front and the ACC showed it was sensing car (car icon lit up). I have used ACC frequently with no other problems.
Wow, that certainly would be unsettling. What setting was your ACC on for distance (you know the spaces that you can cycle through on the center display)? Were you set on close or were you at maximum distance?
Also, something I noticed going through the Rockies was that the cruise control uses more resources for speed control than other cars and in effect keeps you closer to the set speed even at steeper declines. I really noticed when I had the ACC set at 140KPH other vehicles would pull away on declines and I could feel the occasional pulse of the regenerative brakes (at least I am pretty sure that was what it was) to keep my speed regulated. Unexpected but not unwelcome.
I believe there are 4 distance positions. I was at the second closest position. Car was just washed and not many bugs in CA like midwest and south.
I've had instances where car switches lanes in front of me and ACC reacts quickly and in fact most of the time over brakes. It was just one of those situations where you were expecting ACC to slow and suddenly you were in an unexpected situation where collision avoidance was telling to you to brake now!
08-21-2016, 09:34 PM
