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Discussion Starter #1 (Edited)
This morning, there were two accidents along my commute route. This caused a 25-minute commute to become a 90-minute commute.

While in this mess using ACC, the car lost detection multiple times on the car in front of me. (Different cars, so, it is probably not the radar signature.) It therefore didn't stop on it's own as usual. In order to get detection back, I had to back off 50' or so and then the detection started working again as traffic crept forward. The car is clean, so, I don't think there is dirt or something blocking radar or other sensors.

I was trying to get a sense of the conditions that caused the detection miss and it seems that after a few full stops, it just plain lost detection and I had to brake manually (oh, the horror!). The speed was less than 10mph mostly and ACC was doing it's normal thing of closing the gap slowly before stopping.

ACC goes into some sort of creep mode under these conditions. I'm thinking this is to avoid full stops. Then when it resumes from a pedal press or hitting the resume button, it starts off at normal gap setting. IOW, it falls back further than when it came to a full stop. If the car in front stops again (like 1000 times this morning), it closes the gap slowly (what I am calling creep mode) and then stops pretty close behind the lead car's bumper. (The parking sensors don't light up, so, not that close. Maybe 2'.)

Is this normal, or, should I complain to Cadillac?

Edit: to get a sense for how slow this commute was, it took 20min to go the first 10mi and 70min to go the last 10. I usually do the whole 20 miles in 30 to 40 minutes.
 

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This is really interesting. You should contact a Volt/ELR advisor. Seems like your experience could be useful.
 

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In my experience with normal LA traffic it is not normal.
My ACC volt can keep doing this low stop and go stuff for over an hour with many stops.
Maybe a difference between the ELR and the Volt?
 

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Discussion Starter #4 (Edited)
In my experience with normal LA traffic it is not normal.
My ACC volt can keep doing this low stop and go stuff for over an hour with many stops.
Maybe a difference between the ELR and the Volt?
If traffic is moving even a little more than this, ACC is pretty reliable. It only happens when there is a several mile backup and extremely slow speed like inching forward one car length every minute or so. If traffic keeps moving, even at 15mph, I don't see this behavior.

I'm talking parking lot speeds or less. With maybe 30 or more ACC-controlled stops. It's not consistent enough to actually count stops though.
 

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I'm not exactly sure how they implement it, but when everyone's stopped, the radar probably has a real hard time understanding what's what since everything is in the zero Doppler bin of the radar (assuming it is a radar approach they use). (Zero Doppler bin meaning, nothing is moving - road, cars, light poles, buildings, etc. - relative to the radar's movement, i.e. your car).

When things start moving at speeds different than you, or even the same as you, then it's much easier to pick out that target in a given Doppler bin and track it.
 

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This morning, there were two accidents along my commute route. This caused a 25-minute commute to become a 90-minute commute.

While in this mess using ACC, the car lost detection multiple times on the car in front of me. (Different cars, so, it is probably not the radar signature.) It therefore didn't stop on it's own as usual. In order to get detection back, I had to back off 50' or so and then the detection started working again as traffic crept forward. The car is clean, so, I don't think there is dirt or something blocking radar or other sensors.

I was trying to get a sense of the conditions that caused the detection miss and it seems that after a few full stops, it just plain lost detection and I had to brake manually (oh, the horror!). The speed was less than 10mph mostly and ACC was doing it's normal thing of closing the gap slowly before stopping.

ACC goes into some sort of creep mode under these conditions. I'm thinking this is to avoid full stops. Then when it resumes from a pedal press or hitting the resume button, it starts off at normal gap setting. IOW, it falls back further than when it came to a full stop. If the car in front stops again (like 1000 times this morning), it closes the gap slowly (what I am calling creep mode) and then stops pretty close behind the lead car's bumper. (The parking sensors don't light up, so, not that close. Maybe 2'.)

Is this normal, or, should I complain to Cadillac?

Edit: to get a sense for how slow this commute was, it took 20min to go the first 10mi and 70min to go the last 10. I usually do the whole 20 miles in 30 to 40 minutes.
Why would you use ACC in slow traffic conditions? ACC enhances Cruise Control, which you would not use in conditions like that.
 

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Discussion Starter #7 (Edited)
Why would you use ACC in slow traffic conditions? ACC enhances Cruise Control, which you would not use in conditions like that.
Constantly switching between go and stop pedals is tiring. Especially 1,000 times in 10 miles. ACC usually works in these conditions letting me move my feet around preventing muscle fatigue or cramping. It's just this narrow sub-set of VERY slow traffic that is revealing this limitation.

the radar probably has a real hard time understanding what's what since everything is in the zero Doppler bin of the radar
I was thinking that as well. What is the difference between very, very slow and stopped to the system? The cut-off for false positives may be what I am experiencing. There also may be some sort of time-out (several minutes?) where the system turns off the detection icon (and the ability to resume) for some other safety reason. I'm thinking you wouldn't want to accelerate to 70mph or other set point if you're virtually parked behind another vehicle.

I was just polling the forum to see if other people have experienced this with ACC. It's not really that big an issue since it is fairly rare.
 

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Constantly switching between go and stop pedals is tiring. Especially 1,000 times in 10 miles. ACC usually works in these conditions letting me move my feet around preventing muscle fatigue or cramping. It's just this narrow sub-set of VERY slow traffic that is revealing this limitation.
It sounds like you should hire a driver :)
 

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If traffic is moving even a little more than this, ACC is pretty reliable. It only happens when there is a several mile backup and extremely slow speed like inching forward one car length every minute or so. If traffic keeps moving, even at 15mph, I don't see this behavior.
I don't have a Volt with ACC, but I do have a Mercedes with ACC. Following stop-and-go traffic like you describe, it works exactly as expected indefinitely.
The ACC is not designed to handle high-speed driving up on stopped traffic from beyond radar range. But stop and go is exactly what it's *supposed* to do. It sounds like there's something wrong.
 

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Sounds like there is a problem with your ACC. Make sure windshield is clean in front of rear view mirror and all the sensors on the bumper, etc. are clean. One thing I have noticed a car has to be moving for the ACC to lock on it. Thru testing if I have ACC on and no car in front and then you come up on a car ahead of you stopped, it does not detect it and will ram right into it!! One time going around a corner the detector was pointed at a guy walking on the sidewalk, ELR, slowed way down :) Really have to keep an eye on it.
 
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