T6.1 ACC issues with new wheels

[Bga86]

Hi Guys/gals


I wonder if someone has an answer to an issue I’m having, I realise this has been mentioned before and there’s a lot of people who’ve had the issue but no one seems to have posted a confirmed fix for it.

I’ve recently replaced my T6 with a T6.1 T30, it has ACC. I’ve started adding a few bits to it and today removed the standard 16” wheels and fitted a new set of 20” wheels with 275/40/20 tyres on. After driving about a mile down the road I got a “ACC deactivated, sensor impaired fault” on the dash.

Having done some reading it seems this is a relatively common issue, some people are saying it’s down to the speedo not reading accurately and the tyres/wheels need to be smaller some are saying it’s down to the ACC sensor now sitting higher.

I’ve also read that the speedo can be adjusted using vcds, now I have vcds (novice user) but am reluctant to start messing with this as I’ve also read it cannot be put back down on a T6.1 should you change back to smaller wheels.



I appreciate this is a long post but any advice or help would be most welcome please

 

[Drive Wayne]

My 6.1 started doing that when I put a new gloss grille on it. Nasty yellow warning triangle comes on for a few minutes every week on average. Sensor impaired fault, I haven't got ACC. Have you fitted a new grille?

 

[Bga86]

My 6.1 started doing that when I put a new gloss grille on it. Nasty yellow warning triangle comes on for a few minutes every week on average. Sensor impaired fault, I haven't got ACC. Have you fitted a new grille?

Yes I have, the grille was fitted last week and I’ve used it plenty without any faults until the wheels were fitted though?

 

[Drive Wayne]

Yes I have, the grille was fitted last week and I’ve used it plenty without any faults until the wheels were fitted though?

I had 20's on long before the new grille. It wasn't an off the shelf grille, it was a body shop sprayed one. That's the only current warning I'm getting, it's relatively fleeting and it goes away quickly enough, but the grille looks good, I'll live with it!

 

[Bga86]

So I've just put the info into will they fit and it’s showing the speedo will now be under reading quite a bit

 

[Drive Wayne]

70mph on my speedo on my van equates to 74mph on waze.
I'm hoping to collar a wonderful person who uses VCDS at one of the forum gatherings to put mine right, eventually! No rush....! Keeps the miles down a bit!

 

[Dav-Tec]

My 6.1 started doing that when I put a new gloss grille on it. Nasty yellow warning triangle comes on for a few minutes every week on average. Sensor impaired fault, I haven't got ACC. Have you fitted a new grille?

Wayne take the grill off and rub the square area down with scotchbrite to remove the paint. Message or call me if your not sure mate

 

[Dav-Tec]

Also I'm amazed your t6.1 hasn't got ACC

 

[Drive Wayne]

Also I'm amazed your t6.1 hasn't got ACC

It's a Startline, poverty spec! Quote me for ACC Chris! I certainly would like it...

 

[*bigswitch*]

So I've just put the info into will they fit and it’s showing the speedo will now be under reading quite a bit
View attachment 263250

View attachment 263251

Hello, did you get any resolution on this issue?

 

[Macp]

Not had that issue due to wheel change. But I read that a big suspension drop can cause issues.

 

[*bigswitch*]

Just fitted a set of Dirscovery 5 19" alloys with brand new bridgestone 235/55's. Calculation say the speedo will be out by about 10%. no other change was made and the front sensor is clean and unobstructed. The van is also now 34mm higher.

"ACC not activated due to sensor obstructed" comes up intermitently and disables the Cruise Control.

I'm thinking is the speedo being out so much, the radar is confused.

Any info would be appreciated.

Plan is to change the front wheels back tomorrow, to ensure no other issue occurred at the tyre fitters.

TIA anyone

 

[Macp]

Have you had the bumper off at anytime. Or have you tried a reset with a dongle like OBD etc ?

 

[*bigswitch*]

Have you had the bumper off at anytime. Or have you tried a reset with a dongle like OBD etc ?

Nope and nope

AI says:
Key Issues

• Sensor Mismatch: The ACC system calculates vehicle speed based on wheel speed sensors. When larger tyres are fitted, the actual road speed is faster than what the wheel sensors report to the ECU. This can cause the ACC to "stutter," micro-adjust constantly, or throw an error and become completely unavailable.
• Speedometer Inaccuracy: Larger wheels typically cause the speedometer to under-read (e.g., showing 30mph when you are actually doing 33mph), which can lead to legal issues and system faults.
• Irreversible Coding Risks: While it is possible to recode the wheel circumference via tools like VCDS to match the new size, there are documented risks for the T6.1. Some settings are reported to be irreversible—if you increase the wheel variant setting, you may not be able to reduce it later if you revert to smaller wheels.

 

[Macp]

Wonder if thats why im not having issues. At a speedo reading of 30mph, according to willtheyfit.com im doing 28.1mph