[Guide] [T6_modified] T6 Speedo Adjustment with VCDS

[mmi]

Module 17 – Instruments carries also the coding to select a few scaling factors for speedometer.

Byte 0, bits 0..3 have mysterious value “K-number”. It turned out changing this coding adjusts measuring values IDE00842 (K-number) and IDE00845 (Wheel circ. mm) of module 17 - Instruments, and thus adjusts speedo scaling.


I run through all the above coding combinations 01-07 and read the measuring values for each coding combination. The results are in the table below.



Speedo can be adjusted simply by changing the coding. Resulting speedometer delta (vs. factory setting) can be seen in rightmost column, which is actually just a calculation of “corrected” wheel circumference vs. factory value (grayed line).

However, there are some indications that also other factory settings exist...

​

In the case above the change can only make speedo read higher as the van came from the factory with tiny 16” wheels and coding is already at the "lowest" setting of “6”.​

​

Besides factory setting I verified coding values 3 and 4, and indeed speedo is reading way more over. For example, with coding “3” driving at 100 km/h (GPS-speed) the speedo was about 112-113 km/h. At factory coding "6" at 100 km/h (GPS-speed) the speedo reads about 102-103 km/h. As expected these match with the table above (about 9% difference). I think this already is a quite good confirmation that delta values in the table work for the purpose.​

Hopefully members can confirm the table above or just parts of that. Especially interesting would be to see how vans with factory wheels of 17” or 18” are coded and if the measurement values IDE00842/IDE00845 vs. coding are the same or different. Also if any unexpected side effects can be seen in changing the coding… would definitely be nice to know.

​

Just for the record that in VCDS adaptations is a channel “ENG112416-IDE01766 Velocity detection – Distance impulses”, which has value “4”. Changing that didn’t have any effect on above mentioned measuring values. So the purpose of this channel remains unclear, hence request to consider any side effects.​

This tweak is an adaptation from Speedometer Calibration - Page 3

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Edit:
Added a table from a different van.

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EDIT (2022-04-15)

*** NOTE!!! This modification is NOT applicable to T6.1 ***
*** IRREVERSIBLE on T6.1 ***​

T6.1 electronics are based on MQB architecture thus very different than T6.


Unfortunately there are indications that the speedo adjustment on T6.1 is a one-time deal - thus irreversible
Please have a read of the following:

VW Transporter T6.1 2021 Wheel size coding changes issue

Hiya folks! A customer of mine changed his wheels to 20" and wanted his speedo coded to suit the new wheel size. No issue as this is an available change via the "K-Number" coding in 17 Instrument Cluster and done this many times in older Transporters and Amaroks. Well, turns out there is an...

forums.ross-tech.com

2020 MAN TGE (VW CRAFTER2), Coding BYTE3 in Control Unit J285 can not be undone

Hello VCDS community, first I have to thank Uwe for this great tool (VCDS), which gives me so many opportunities with the car. I love it. Thank you very much for that. :thumbs: A short introduction to my person. My name is Thorsten and I am an electronic engineer and computer guy from Germany...

forums.ross-tech.com

 

[Adrian72]

Is there anyone in the manchester area who would be willing to do this for me? my speedo currently under-reads (says 25mph when doing 30mph) I've double checked it against Sat-Nav and phone app.
And I suffer from Road Rage frequently because of it

 

[Shredder]

Due to my ignorance of this technical area .... forgive the simple question.

In my mind I have distilled this down to :

You input your data into 'willtheyfit.com', as we all know, one of the parameters fed back to you is the % speedo error caused by your new set up. You then give that % error to a whizzo VCDS boffin who can pretty much correct your speedo as near as dammit.

Am I being too simplistic or is my logic correct ??

Otherwise, I'll have to continue with my great little App 'Speedometer (Pro)' displaying true speed on the 'Droid

 

[mmi]

Thanks, yes, exactly as you said. As soon as required correction is known the VCDS can do the job.

Anyways, a slight pitfall being that the T6’s seem to come with different factory codings and different corresponding wheel circumference tables behind as the tables above show. There the VCDS comes to help being capable of verifying the result from coding change right there.

The process would be:

1. Define the correction % needed.
2. Check and record the factory coding of your van (in the tables above leftmost column, value in range of 1-7)
3. Read and record corresponding factory measurement value IDE00845 (Wheel circum.)
4. Change the coding (initial guess would be from the tables above).
5. Read and record measurement value IDE00845 again.
6. Verify achieved correction factor by calculating the change% by dividing value from (5) by value from (3).
7. If not happy with the result % try different coding = go back to (4).
8. And the most important part: Post the values from (2), (3), (4), (5) here please .

Of course the coding change can be done with other tools, too.

 

[Shredder]

That's a very comprehensive answer thankyou @mmi

Of course, I'm man enough to admit I don't fully understand it but the great news is that it appears my simplified view can be achieved.

One question. According to 'willtheyfit.com' .... my speedo is - 5.18% out. The second table in your post above suggests that once you get beyond -2.1% error you can't correct it,saying "out of range" ....... or is it just because I'm not familiar enough with it??

Now, I just need to find someone who can provide a VCDS service at this level

 

[mmi]

Thanks. Yes, the challenge is not to get confused with speedo reading, correction, speedo error with new wheels, etc. in which way they work.

In the tables above my simplified approach was to look only how coding change affects speedo reading. So changing (table 2) coding from factory setting “4” to “3” will just make my speedo read more – at certain speed at factory setting "4" speedo would read 100 units and after coding to “3” speedo would read 104 units at the same speed.

Anyways, the bottom line is that for bigger wheels you need to make speedo read more, that is “+” values in the table. Thus giving actually a couple of choices for bigger wheels.

For smaller wheels – use "-" values of table, unfortunately not much to do .

As “willtheyfit.com” tells that speedo error is -5.18% your wheels are significantly bigger than factory wheels (also revealed by your avatar) – so the correction choices (if table 2 applies to your van) at first glance would be +4.0% or +7.8%.

I think EU regulations has forced speedos read over a little. I have observed about 3% error in T6 vans. They have been reading 103 when real speed is 100 with factory wheels.

So for you the setting +4.0% definitely would be better match – taking away some of the EU tolerance. Speedo reading would be about 2% more than actual speed – at speedo 51 when real speed is 50.

The correction by +7.8% would make your speedo very optimistic – showing about 53 when actually doing only 50.

Currently with your bigger wheels I think that your speedo under reads about 2%. At speedo reading 50 your real speed is 51. Have you checked this?

Just a note that the change affects also odometer reading, and thus your fuel consumption readings - improving them, as seemingly you are doing more miles .

Yes, correct, the “out of range” means that the controller does not accept those coding values. So nothing available there.

 

[Shredder]

@mmi .... this is just fantastic thank you !

I pretty much get what you are saying there and your guideline recommendations for what the VCDS operator has to do are very clear.

I see what you mean about the options and I agree the +4% option is more than satisfactory from your explanation. However, I am using the speed estimates from 'willtheyfit.com' and as you suggest, next time I am in the van I will switch on my GPS speedo App to see if my van has both the error from the wheels AND this EU error you refer too.

Thanks again

 

[Shredder]

Well … a very unexpected turn of events @mmi

Taking your advice to check 'actuals'. I used 'speed-ometer (Pro)' on Android. Your forecast based on EU tolerances was correct. The speedo (when compared to GPS tracking using this App) is actually pretty much correct with the 20" rims on

It's about 1 mph out around the 50mph mark and about 2 mph out around the 80mph mark.

No speed correction needed after all and as you indirectly inferred, 'willtheyfit.com' is mathematically correct forecasting MPH on the laptop but incorrect in the real world

Extremely valuable and useful thread thank you

 

[Glenn Board]

Hi, the tyres that i have fitted and subsequently causing the issue are 235/65R17 108H Yokohama Geolandar A/T (G015) if its not too much trouble what byte in the VCDS would you recommend please?

 

[mmi]

Hi, the tyres that i have fitted and subsequently causing the issue are 235/65R17 108H Yokohama Geolandar A/T (G015) if its not too much trouble what byte in the VCDS would you recommend please?

Unfortunately it seems that there are different tables for speedo adjusting among T6s - the both vans I checked were different. So it is impossible to answer your question without actually checking by VCDS what values (IDE00845 wheel circumference) are available in your van and what the current setting (Byte 0) is.

-> Check in codings what current K-number (Byte 0) is, and then read at measuring values the corresponding IDE00845 (wheel circumference).​

In the other thread I understood that with your new wheels your speedo is now right on spot? It is not possible to change odometer scaling independently from speedometer.

 

[Glenn Board]

Thanks, so it looks like changing any of these setting to what is correct for tyre sizes will alway have the speedo over reading as standard. I am really stuck on how to correct this using VCDS, would you be able to help with some more detailed instructions and a guess of which setting to use please?

 

[mmi]

Thanks, so it looks like changing any of these setting to what is correct for tyre sizes will alway have the speedo over reading as standard. I am really stuck on how to correct this using VCDS, would you be able to help with some more detailed instructions and a guess of which setting to use please?

Yes, the main question is which one you need to read “more correctly” with new wheels, speedometer or odometer.

The speedo offset from factory probably comes from EU-regulation. The speedo is set to read a little more than actual speed (can’t blame speedo for speeding). I think the odometer is pretty close to actual, although I have no way to really verify that accurately. Anyways, what I have noticed the odometer reading is quite close to google-map measurements - if that proves anything.

Generally, changing Byte_0 coding to smaller number (for example from 6 to 5) should change your speedo and odometer to read more. But as the tables above from different vans show – how much, it depends…

Just to clarify that the coding change will change both speedo and odometer reading by same percentage. So if you now have your speedo reading correctly, any change would take that away.

Anyways, to solve this the following are needed

1. factory wheel size,
2. new wheel size = 235/65R17
3. factory coding
4. correction needed

The VCDS process would be the following:

Step 1. Make a backup of your van's settings using Auto-Scan



Step 2. Select control module 17-Instruments



Step 3. Read current measurement values


....

Step 4. Read current coding




Step 5. Change coding of K-number (above)

Step 6. Reread measurement values = new wheel circ. & K-number



To complement information in this thread would be nice if you could go through all the available coding values (step4 - K-number) and read corresponding measurement values please (step 6). That would help to define new coding without guessing.

 

[Glenn Board]

This is too helpful, thank you really appreciated, i will do it the weekend.

 

[Glenn Board]

sorry to bother you again, so you have worked this out based upon the dimensions of my new tyres on the standard VW Wheels?

 

[mmi]

sorry to bother you again, so you have worked this out based upon the dimensions of my new tyres on the standard VW Wheels?

Sorry, but no, as I don't know what was your original tyre size (215/60-17 perhaps?). Also we are missing the corresponding value for wheel circumference stored in location IDE00845 at step 3. So at the moment we have nothing to compare with your new tyres.

Would be helpful if your could go through just steps 1-4 and post the results here...

Then step 5 would be just change the value "xx K-number, K-number x" by one and reread corrected values in step 6. The tables at the top were created repeating steps 5-6 with all available values of "xx K-number, K-number x"

By comparing with 235/65R17 with 215/60-17 at Will They Fit - Online Wheel and Tyre Fitment Calculator the correction should be 6.4%. So depending which table (at the top of this thread, long coding, byte 0, bits 0..3) your van currently has you should change change coding by "1" or by "2" units smaller than the current (step 4 - either from 6 to 4, or from 4 to 3, depending what the original value is).

The screenshots above are just to show which way to go and on what buttons to click - but actual values we have not really determined yet. As you might have noticed, the coding value in screenshot (step 4) was yet another one (not a standard one but based on tyre size 235/55-17 to correct my speedo display).

The thing that bothers me is quite big error in your odometer reading (8%, from the other thread) but the speedo reading correctly. The few vans I have had my hands on, have had after speedo adjustment to show correct speed, odometer to read only about 2% less actual distance (well, only can compare with google maps route calculation) - which happened to be the same amount as with the speedo was corrected. Which to me implies that odometer is quite close to actual distance with factory wheels.

 

[Glenn Board]

Thanks, i will do the weekend, really appreciated.

 

[Glenn Board]

Hi, and sorry for delay, I have now been through to step 4 and have enclosed the relevant screenshots, considering these, how would you advise I proceed and what values would i need to change please?

Thanking you in advance, this is al really helpful.

 

[mmi]

Almost there. Now we know how your van is coded (Distance Impulse Number = 7).
Sorry forgot to mention that you need to "tick boxes" for those two measurement value to get the needed values (wheel circumference).


Then the needed values appear in the other window - as example below


Could you please provide these.


- - - - -
The next step would be to change the coding to "06 Distance impulse number 6..." and read again the two values above.

Then "05 Distance impulse number 5...", and read again the two values above.

Going through all the values "07..." - "01..." will reveal what is possible in the van.

As your van is coded differently than either of the vans in the first post, I think we need to create similar table for your van.

Hope this helps...

 

[Glenn Board]

Hi, how is this, what would you advise next please?

 

[Glenn Board]

so i suppose the next step to to know what the wheel circumference is, and what is the K number?