Front assist/ACC intermittently unavailable

[coolhandluke]

Hi all,


I bought a 22-plate van from a VW Van Centre around 7 weeks ago. It had only done 8,000 miles, but within the first 3 weeks I noticed a few issues that meant it had to go back to them for repair.
They’ve now had it for 4 weeks, and I’m due to get it back later this week once the rear window has been replaced due to water ingress into the tailgate body.

One of the issues I reported was the Front Assist / ACC intermittently showing as unavailable. It doesn’t happen all the time, but on longer journeys (50+ miles) the warning would pop up several times. On other occasions, including using ACC on A-roads on longer runs from Shropshire to the Mid Wales coast, it’s worked absolutely fine.

The Van Centre rang me this morning to say their technician can’t find any fault with the sensor or the system itself, but he believes the issue may be caused by the grille that’s fitted. Apparently, because it has been painted, they think the paint thickness may be affecting the Front Assist / ACC operation, albeit only intermittently.

They’ve offered to replace it with a standard grille, but the van has quite a bit of black styling already fitted - Leighton rear bumper/spoiler, black side bars, matte black grille etc - so swapping it out would spoil the overall look a bit (picture below).

I’d rather avoid that if possible, and to be honest I can live with the Front Assist / ACC occasionally not working as expected, especially as I know warnings can sometimes appear anyway in heavy rain, snow, or after road impacts.

My questions really are:

• Is an aftermarket or painted grille a known cause of intermittent Front Assist / ACC issues on these vans?
• Has anyone else had similar problems with a painted grille affecting the radar/sensor?
• Also, if the warning only appears intermittently, is this likely to cause any MOT issues going forward?

Any advice appreciated.

 

[Bav]

I've got a gloss-black grill on my van and it doesn't cause ACC issues.

The ACC did throw a wobbler once, when driving through a section of single-lane contraflow traffic wirh large cones down either edge of the lane, but nothing else in the past 3 years.

 

[Salty Spuds]

It "Might" be a wheel speed sensor that's on the blink. It needs plugging in and any fault codes reading before we can give any meaningful advice, otherwise we're just guessing. There are many seemingly un-related causes of the ACC being un-available, one of which is a faulty trailer brake light. Go on, ask me how I know

 

[coolhandluke]

I've got a gloss-black grill on my van and it doesn't cause ACC issues.

The ACC did throw a wobbler once, when driving through a section of single-lane contraflow traffic wirh large cones down either edge of the lane, but nothing else in the past 3 years.

Ok so sounds like they're fobbing me off then. I'll look at getting VCDS and check the codes myself.

 

[Bav]

Ok so sounds like they're fobbing me off then. I'll look at getting VCDS and check the codes myself.

Thinking about it, my grill is aftermarket rather than OE painted. Not sure if that would make a difference.

 

[Fairy Cringe]

I’ve got pretty much the same van as you and yes, my ACC had a bit of a wobble and became unavailable. I bought a plug and play diagnostic tool from Amazon (Topdon), works in conjunction with Carpal app loaded on my iPhone. Sure enough the fault was highlighted but also cleared without drama. It’s behaved itself since (4 months).

Had a technical dig and as a precautionary measure I have renewed key fob battery and ensured that the main vehicle battery voltage remains high and healthy. Apparently these two points can cause havoc with ECU miscommunication. Low hanging fruit, easy to cover.

 

[Fairy Cringe]

Oh, and I have the Leighton workover too. Bumpers, grills etc.

Personally I lean on my ACC quite a bit, particularly on euro runs. I missed it when it was playing up…

 

[archersam]

I have a painted grill and no issues, the only thing that impacts mine is slush and snow.

 

[coolhandluke]

I’ve got pretty much the same van as you and yes, my ACC had a bit of a wobble and became unavailable. I bought a plug and play diagnostic tool from Amazon (Topdon), works in conjunction with Carpal app loaded on my iPhone. Sure enough the fault was highlighted but also cleared without drama. It’s behaved itself since (4 months).

Had a technical dig and as a precautionary measure I have renewed key fob battery and ensured that the main vehicle battery voltage remains high and healthy. Apparently these two points can cause havoc with ECU miscommunication. Low hanging fruit, easy to cover.

Thanks for this. I'll take a look at the diag tool you mention. VCDS and OBD11 appear to be the tools of choice for most folks. Any reason why you went with Topdon/carpal ?