Adaptive cruise control fault?

[JasonM]

Hi, Recently acquired a Corolla touring sports 23 which has been great so far apart from some issues I’ve had with the ACC.  95% of the time it works perfectly but occasionally when approaching a slower vehicle the ACC slows my car to the same speed as the car in front  then shuts down and stops tracking the car in front.  I then have to tap the accelerator pedal to re-engage the ACC otherwise the car would just slow down to a stop which can be dicey on dual carriageways.  Is this meant to happen as first car I’ve had with ACC and seems like it could be a fault?  

[sportse]

Do you mean in stop start traffic?

it’s normal to do that if so, it will disable acc temporarily after you are stopped for a few seconds. You then have to either tap the accelerator or press resume to get it to start working again. 

[JasonM]

Hi, No in flowing traffic, say I am driving at 70mph and car in front driving at 60mph, as I approach my car slows correctly and then just switches off with no engine power.  Green light on dash stays on but car cruise control unavailable and needs me to tap accelerator pedal to resume.  Seems to happen more on downhill gradients.  Took it to my local dealer and they drove the car and said all fine buts it’s annoying as only happens intermittently.  

[sportse]

Does it happen with different following distance settings?

Occasionally I'll override mine with the accelerator because it drops back too far - usually also going downhill on a curve.

[JasonM]

Thanks for your feedback, I’ve not tried adjusting the distance control as tend to leave it on 3 bars and only really use the ACC on dual carriageways but will give it a go.  Your experience on hills and curves seems to to tally with mine.  Also found this on a Corolla cross forum so seems like it might be something I just need to accept and get used to.

https://www.corollacrossforum.com/threads/corolla-cross-hybrid-safety-sense-3-0-dynamic-radar-cruise-control-issues.608/

[Cyker]

I don't recall my one disabling itself like that while slowing but still moving (Albeit it's a Yaris not a Corolla), only if it actually stops, but I don't have much experience because I always cancel the ACC when approaching a slower car as the ACC just doesn't know what to do - Very often, it'll maintain the same speed for too long instead of coasting down, then it'll suddenly notice it's closing in on the car in front and engine-brake very harshly, then accelerate harshly again as it 'overshoots' its braking and drops too far back and tries to catch up again.

It's okay if the car in front is slowing very very gently, or is a truck, but especially if you're coming up on slow moving traffic it really doesn't work very well.

[JasonM]

Yes I know what you mean and the problem seems to be made worse when running down hill approaching a slower car.  Having had a manual car previously without almost any driving aids I think my expectations are probably unrealistic and more intervention will be needed from the me from time to time.  I have only had the car for a few months so still getting aquatinted with it’s foibles..
 

[Cyker]

To be fair it just reinforces the fact that it's an "Assist" and not full self-driving - For the most part it works pretty well within its limitations.

 

[JasonM]

👍

[Roy124]

50 minutes ago, Cyker said:

To be fair it just reinforces the fact that it's an "Assist" and not full self-driving - For the most part it works pretty well within its limitations.

And sometimes the "Assist" is unwanted as the computer will override the human. 

The classic intervention is the rear crossing alert.   The driver can see an obstructing vehicle has crossed clear and is receding soon than the computer.  The computer then forces a stop.