ACC losing 'lock'?

[FelisBengalensis]

Anyone else with ACC finding that it will randomly suddenly lose radar lock on a vehicle ahead and will suddenly accelerate requiring rapid brake application to stop the car?

For as yet unclear reasons and completely at random on perfectly clear days (so no rain in the sensor) my car will suddenly lose 'lock' on a vehicle in front in a queue of traffic and try to accelerate up to the set speed even though the vehicle ahead may be less than 3 metres ahead. There is no consistent set of conditions which seem to cause this, or any specific vehicle type. I have had to jump on the brakes several times in recent weeks to prevent the car rear ending something ahead! My faith in it as a tool is being sorely tested. I'm conscious that driver aids come with huge manufacturers caveats and always keep my foot hovering over the brake pedal.

I can only assume that mine may be faulty though getting a Dealer to accept it might be an even bigger challenge.

Anyone else experienced this with their ACC system?

[Alf01]

We have just had ours for a months but my wife has done a 1200km round trip to Brisbane and every time I used it, it worked flawless.

Check that your radar on the grill is clean and your windscreen at the top where the camera is mounted is also clean.

Assuming that all of them are fairly clean, it's time to take it back to the dealer and have it checked. If there is an issue, it should throw up a fault code that the dealer should be able to download.

[999pooch]

Had 2 VAG cars over 2 years & 20k, never had this problem.

Occasionally if the 'object' car drifts slightly over to the left and you have a slight right hand steer it can loose lock, but assumes you are overtaking / manoeuvring around the object.

Sounds more like a fault or may need re- calibrating.

Edited 12 September, 2016 by 999pooch

[RickTT]

Do you get the apply brake message popping up as a warning when the car in front is slower and your car is slowing right down ? 

 

Is the green LED lit when you find your self catching the car in front up ?

[Leeboy]

Not had such a problem you describe but do sometimes find it will allow undertaking and other times will not when traveling through 50mph narrow lane motorway roadworks. Haven't been able to identify the circumstances that are particular to allowing the car to travel faster in the middle lane than say the outside lane when traffic ahead is clear.

[Leeboy]

Not had such a problem you describe but do sometimes find it will allow undertaking and other times will not when traveling through 50mph narrow lane motorway roadworks. Haven't been able to identify the circumstances that are particular to allowing the car to travel faster in the middle lane than say the outside lane when traffic ahead is clear.

[Defenderben]

Sounds faulty - get it booked in for checking.

Had 2 x VAG cars with ACC never had that issue.

[BillyJim]

Not had such a problem you describe but do sometimes find it will allow undertaking and other times will not when traveling through 50mph narrow lane motorway roadworks. Haven't been able to identify the circumstances that are particular to allowing the car to travel faster in the middle lane than say the outside lane when traffic ahead is clear.

50 mph is the cut-off point. If the offside vehicle and your vehicle are below 50 mph it allows you to pass on the nearside without hindrance.

[BillyJim]

Anyone else with ACC finding that it will randomly suddenly lose radar lock on a vehicle ahead and will suddenly accelerate requiring rapid brake application to stop the car?

For as yet unclear reasons and completely at random on perfectly clear days (so no rain in the sensor) my car will suddenly lose 'lock' on a vehicle in front in a queue of traffic and try to accelerate up to the set speed even though the vehicle ahead may be less than 3 metres ahead. There is no consistent set of conditions which seem to cause this, or any specific vehicle type. I have had to jump on the brakes several times in recent weeks to prevent the car rear ending something ahead! My faith in it as a tool is being sorely tested. I'm conscious that driver aids come with huge manufacturers caveats and always keep my foot hovering over the brake pedal.

I can only assume that mine may be faulty though getting a Dealer to accept it might be an even bigger challenge.

Anyone else experienced this with their ACC system?

ACC wil not detect already stationary traffic if travelling above a certain speed. I don't recall the exact speed but it's quite low - 20 mph?

That doesn't appear to be the example you describe so I'll follow the crowd and say there's a fault with a serious safety implication.

I've been using ACC for a year whenever practicable and it has been faultless (as I now rush off to touch wood).

[Coops]

Anyone else with ACC finding that it will randomly suddenly lose radar lock on a vehicle ahead and will suddenly accelerate requiring rapid brake application to stop the car?

For as yet unclear reasons and completely at random on perfectly clear days (so no rain in the sensor) my car will suddenly lose 'lock' on a vehicle in front in a queue of traffic and try to accelerate up to the set speed even though the vehicle ahead may be less than 3 metres ahead. There is no consistent set of conditions which seem to cause this, or any specific vehicle type. I have had to jump on the brakes several times in recent weeks to prevent the car rear ending something ahead! My faith in it as a tool is being sorely tested. I'm conscious that driver aids come with huge manufacturers caveats and always keep my foot hovering over the brake pedal.

I can only assume that mine may be faulty though getting a Dealer to accept it might be an even bigger challenge.

Anyone else experienced this with their ACC system?

 

Yes I've had this problem.

 

It first occurred after the car had been sat all day (in quite warm & bright conditions) - it would come to a halt then suddenly accelerate forward, and like you, I had to jump on the brakes quite quickly. It did this 2 days running and despite resets each day it would keep doing it.

 

However, after that it hasn't done it again, but I still find myself hovering over the brake pedal!

[5er]

Also had some similar experiences. In my case it happened when in stationery traffic, and left some more space before moved on, in one case also someone jumped into that space, but was then stationary there, then when I touched the gas pedal to move on, it would start accelerate to the set speed (30kmph) and I had to jump on the brakes not to hit the car in front. First time it was so close I also got the collision warning. In regular driving never had any problems.

[Rainmaker]

I've only ever had the opposite problem; random emergency stops! The worst one was on the approach to an ATS enforced by a red light camera. Green light, 60mph, and a few yards before the stop line the ACC performed an emergency stop, then just before we came to a halt it floored it again. Not another car in sight, and luckily the lights stayed green else it'd have gotten me a ticket.  Mine was seemingly cured after wiping a couple of bugs off the radar sensor, but I'd definitely get yours booked in mate. 

[FelisBengalensis]

It always happens when already in a stop/start queue of traffic approaching junctions. Done it four times recently but then been perfect since last week. No rain, radar sensor & camera both clean, green symbol on, little car symbol on the cruise control lock indicator just vanishes even though the car is still in front. System thinks the road is clear and off it goes!

I think I'll get it looked at.

Thanks to everyone who took time to comment/query/suggest things etc. Much appreciated :-)

[Csory]

Just found this thread and was wondering if it is the 160 or the 210 version? The radar units are supposedly different with the latter operating on a tighter beam afaik - easier to "loose target"?!

[BillyJim]

The 160. The 210 version is not an option in the U.K.

[Csory]

If only an expert could chime in and confirm if (and if then what...) are the differences between the two units? Also, it would be interesting to see if there is a correlation between the "never had a single glitch" and the "scares me every now and then" folk. Since this community is from all across Europe maybe we can figure out if the 160 units are more prone to this than the 210?