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I can see this is an old thread but I've recently had the same "ACC Limited Availability" warning when towing my 1800 kg MTPLM caravan with a 2019 Touareg R-Line with rear coil springs. I got the car in February after trading in a 2017 Touareg with the same suspension that I towed the same caravan with around the UK and France without any problems.

It didn't happen the first two tows but did towards the end of a trip to Ludlow where the last part of the journey was on a section of "A" road that had some fairly severe undulations which caused the car to pitch (see-saw) a fair bit.

A few days later after driving a while it reset but occurred again on the journey home via a different route avoiding the undulating road. Afterwards I researched the issue on several forums and discovered how to determine the front centre radar (behind the VW emblem) angles with VCDS to find that the vertical was +1.196 deg which was outside the +0.8/-0.8 tolerance. The radar mount has two adjusting screws, one for horizontal and one for vertical angles so I adjusted the upper by one full turn clockwise. During an 11 mile test run the ACC error reset so I again checked the vertical alignment and it had reduced to +0.451 deg which was within tolerance. I subsequently gave it another clockwise turn on the vertical adjuster which has pretty well zeroed the setting. The ACC is operating without problem but I'll be towing again shortly so will be interested to see if the problem returns.

It could be that the radar setting was close to the + limit and the effect of the caravan nose weight was enough to cause the error. My caravan nose weight is probably around 110 to 120 kg so within the VW specification for the car. I've since been trying to find a suspension upgrade option like MAD spring assisters but nothing suitable so far.
I hate to say it but if you've adjusted the radar mount you've stuffed it. It will now need to be recalibrated by the dealership using a rather elaborate calibration unit. It's not as simple as putting it within tolerance using VCDS.

There's an update for the front camera and Front Assist systems, which addresses ACC failures. Check with your dealer if TPI 2054374/4 has been carried out on your car. It's an update in two parts, an update for the nav system and and update for the driver assist systems controler. No calibration required post update so you going to have to address that separately somehow. It's about £400 if you need to pay for it..
 

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I've had the Front Assist error message appear on my car a number of times. It mostly happens when Solo but has also happened when towing.

I've never carried passengers in my treg and it is never that heavily loaded. It also has Air Suspension so I'm not sure it is necessarily to do with loading up the rear end of the car.

One time it happened we were driving directly toward the sun and another time we had just left home in the spring and the there was some ice on the sensor. In both cases it started working again on its own. Don't remember details of the other times but I'm pretty sure it always starts working again with doing anything.

edit: just remembered one other occasion, which was when towing - we were following a truck on the motorway and there was a lot of spray coming off the tyres as it had just been raining.

So it seems that, in my case at least, the problem almost always occurs when the sensors are 'blinded' by something. Not saying that is always the case for everyone of course.
 

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Mine also failed on a frosty day but then continued to fail thereafter. Hadn't been an issue prior even when towing and I also have air suspension. In for a service and the dealer recognised the fault and also couldn't clear the stored error.
They ran the TPI I mention above. No issues since
 

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2016 Touareg 3.0 TDI 262. Factory Towbar
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We have a 2016 touareg, and have experienced electronic malfunctions when towing our twin axle caravan over long distances. I checked the handbook, and found that any overloading of the wattage going through the 13 pin socket will cause electronics problems. Our large 2 door fridge takes 170 watts when on 12 volts, so I tried towing with the fridge switched off and this not only completely cured the problem, it enabled the ATC to work faultlessly, which had also been causing problems. I found that if the fridge was frozen down well before the journey, it was still frozen on arrival, and also could be topped down on gas during a part- journey stop. Hope this helps anyone with similar problems.
 

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VW Touareg 3.0L V6 CR7 R-Line
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I hate to say it but if you've adjusted the radar mount you've stuffed it. It will now need to be recalibrated by the dealership using a rather elaborate calibration unit. It's not as simple as putting it within tolerance using VCDS.

There's an update for the front camera and Front Assist systems, which addresses ACC failures. Check with your dealer if TPI 2054374/4 has been carried out on your car. It's an update in two parts, an update for the nav system and and update for the driver assist systems controler. No calibration required post update so you going to have to address that separately somehow. It's about £400 if you need to pay for it..
@fka
Well all I can say is that I've done over 1500 miles since adjusting it, about 300 of that towing and all systems are working with no warnings or errors. I use the ACC a lot and it's fine, working perfectly.
 
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