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Hopefully one day a FORSCan update will give us more options, for now they added a new larger size (2260) which gets us closer. I was hopeful when I saw the use customer tire size option but then there was no place to enter what that is.

View attachment 134084

I don't have the forscan software and hardware yet but years and years ago I was down to edit some source code. It is my understanding that forscan lets you dump your current vehicle bcm config to a file. Can you (or anyone) give me a copy of your vehicle file (if it doesn't contain anything personal like your VIN). I would like to poke around in it. I suspect that the mm per rotation value may be something that could be set directly and you might not even need forscan to do that, a simple hex editor might do depending on the file encoding.
 

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That's along the lines I was thinking. If you dump the file with a known value for tire circumference, then change the circumference and dump the file again, it should be possible to see where that hexadecimal is saved.
 

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I don't have the forscan software and hardware yet but years and years ago I was down to edit some source code. It is my understanding that forscan lets you dump your current vehicle bcm config to a file. Can you (or anyone) give me a copy of your vehicle file (if it doesn't contain anything personal like your VIN). I would like to poke around in it. I suspect that the mm per rotation value may be something that could be set directly and you might not even need forscan to do that, a simple hex editor might do depending on the file encoding.
Forscan will let you edit the raw hex file if you dare. The section we edit is predined hex editing for dummys. It maps changes we make in plain english and changes the hex file accordingly.
 

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Discussion Starter · #84 ·
Here are instructions for getting your vehicle's As-Built file direct from Ford:

PS: I found this several days after bricking Wifey's van and dropping it off at the shop to restore it once I loaded my 2015's file to get it at least running, lol
 

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Yes, post #27. Tire circumference seems to be the key to make the change. Both mph and odometer are adjusted.
Thanks Andrew. I followed these steps and it adjusted my speedometer. HOwever, I now have a DTC p1635 Tire/Axle out of Acceptable Range. I reset everything to factory, cleared codes. Its still there. Any thoughts?
 

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Thanks Andrew. I followed these steps and it adjusted my speedometer. HOwever, I now have a DTC p1635 Tire/Axle out of Acceptable Range. I reset everything to factory, cleared codes. Its still there. Any thoughts?
I was able to go to 2260 on my 2017 cargo, and didn't get any codes. In fact, a reoccurring P051b has stopped showing up since I've read the BCM.

just thinking out loud...

Which circumference did you go to, and what year is your Transit?
Have you tried going to a smaller number to see if it clears?
 

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Discussion Starter · #87 ·
I followed these steps and it adjusted my speedometer. HOwever, I now have a DTC p1635 Tire/Axle out of Acceptable Range. I reset everything to factory, cleared codes. Its still there. Any thoughts?
That's new to me, and my changes are beyond the main solution of changing rolling circumference.
 

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I didn't get any codes after changing mine to 2260 either. I do have a recurring P051b code, and the tire circumference change hasn't had any impact on that. I've narrowed down how to reproduce that code (about 90% of the time) - start with a cold engine on a cold morning, warm up by idling in the driveway. Once warmed up, shut the engine off, then restart within about 2 minutes. Boom, code P051b...
 

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... I do have a recurring P051b code, and the tire circumference change hasn't had any impact on that. I've narrowed down how to reproduce that code (about 90% of the time) - start with a cold engine on a cold morning, warm up by idling in the driveway. Once warmed up, shut the engine off, then restart within about 2 minutes. Boom, code P051b...
Yup, that sounds about right... I'm wondering if I'm just lucky as it's getting warmer here :)
 

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I was able to go to 2260 on my 2017 cargo, and didn't get any codes. In fact, a reoccurring P051b has stopped showing up since I've read the BCM.

just thinking out loud...

Which circumference did you go to, and what year is your Transit?
Have you tried going to a smaller number to see if it clears?
My van is 2018 and the 3 changes I made were:

tire size set to use customer dimension
circumference set to 2260 mm
speedometer bias set to 02

I didn't change the drive ratio.

I have reset everything to factory, but code is still there
 

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My van is 2018 and the 3 changes I made were:

tire size set to use customer dimension
circumference set to 2260 mm
speedometer bias set to 02

I didn't change the drive ratio.

I have reset everything to factory, but code is still there
Did you happen to notice if that code was present before you did anything to it at all? My 2017 had that code before and after I made these changes. My guess is it will go away when we can finally input our actual tire size. Until then, it will always be out of expected ratio because it's either looking for the factory tire size (which our tires aren't) or the 2260 mm size (which our tires still aren't).
 

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My van is 2018 and the 3 changes I made were:

tire size set to use customer dimension
circumference set to 2260 mm
speedometer bias set to 02

I didn't change the drive ratio.

I have reset everything to factory, but code is still there
To clear codes, changing settings back to factory won't do it.

You have to actually clear the DTC using a code reader or ForScan.
 

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To clear codes, changing settings back to factory won't do it.

You have to actually clear the DTC using a code reader or ForScan.
Good point. I know in my case I reset my DTCs because it shows a history of your DTCs and it showed an old MAP sensor DTC I'm assuming was related to driving my van up my driveway with my air box removed after I pulled it to mount an air compressor. The out of ratio code did reappear for me after clearing them though.
 

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Did you happen to notice if that code was present before you did anything to it at all? My 2017 had that code before and after I made these changes. My guess is it will go away when we can finally input our actual tire size. Until then, it will always be out of expected ratio because it's either looking for the factory tire size (which our tires aren't) or the 2260 mm size (which our tires still aren't).
No codes before. Very odd. Rest everything back to factory and cleared codes. Multiple times. its still there.
 

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I got my trial extended license and altered the wheel circumference today from 2160 (37) to 2260 (57). At least 37 / 2160 was the option highlighted so I am guessing that was the current setting. I am not sure if the tire shop would have changed this when I got 245/75/16 K02's back in December. I would have expected a slightly smaller value from the factory.
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No codes but I can't test right now since the van isn't drivable for unrelated reasons.

@Mitch did you make any progress trying to diff the main BCM before and after a change? Happy to help with this including uploading a before and after. I have software and electronics experience but it's my first day using FORScan so I need to figure out even how to dump the relevant part of data. I am curious if the decimal option code (e.g. 37 or 57) are actually what are encoded and the speed/odometer calculation is handled elsewhere.

I'll probably try to dump before and after data at some point this weekend and see if I can start understanding how it works but if I'm re-inventing the wheel (no pun intended) I'd happily take a pointer in the right direction.
 

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Oh forgot to mention, my van was delivered with a 3.31 final drive but it's a 3.73 locker now. I chose that ratio to more or less cancel out the larger tire size to end up with a similar RPM at a given speed. My reasoning is that if I had just dealt with the 10% speedo error, the final drive shift points were probably fine. But now that I changed the speedometer to reflect a larger wheel, maybe I should change the ECU final drive to 3.54 or even 3.73? Increasing the final drive ratio in the ECU would lower the shift points, right? Of course my van weighs about 8200 lbs so maybe having higher shift points is better so the engine isn't lugging and getting poor fuel economy? Or is my thinking backwards?
 

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Discussion Starter · #97 ·
Give the final drive change a try. I adjusted my final drive ratio and it seems to perform differently than our other almost identical wagon (but with stock tires), yet have no conclusive data to show an improvement. Both are 3.5 EB with 3.31 rear ends.
 

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@Mitch did you make any progress trying to diff the main BCM before and after a change? Happy to help with this including uploading a before and after.
I got a scanner in but have not played with it yet partually because I still need to resurrect my old windows laptop, but also because I got orders to Miami! So I am going to be PCSing down there in a month and don't really want to muck with the van before an important trip like this...

Would gladly take you up on your offer of diffing the files.

Two files would be great, only changing the tire circumference between them.
 

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Took several readings for different tire dimension settings this morning. NB: my method was not even to reprogram the van, but make the change to tire dimension in the UI and then click “Save”. Saving gave me a '.cct' file that looked like this (the below is for 2260 mm tire dimensions). (Guessing my VIN is encoded in block 1 but I don't mind sharing that much.)

Code:
;Block 1
FE00318273713030350D0A3146545952325847364A4B4131393434310D0A0000000000000000000D0A0000000D0A0000000000000D0A00000D0A0000000000000D0A00000000000000000000000000000000000000000D0A
;Block 2
00000000000000000000000000000000000000000000000000000000000000000000000000000000
;Block 3
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
;Block 4
FC6F
;Block 5
650901002A01030149020901010100020001000101010101000101000204000201020202010001010002070101000100000057000001000103010101000900010100010E104645010401080100020130010001000101000102000000110000010101040005010001000100000302000A00000100000100000000020101000102000003000002000201020201020001040101040202000000000100000100010000000000000000000002000100000000010100010000000001010100000101010002000200010100000000000000000000010100000100010002030000010001010000000000050000000100000001010000010100000000000030440000
I did this for several different sizes and came up with a small chart. Unfortunately all that really seems to change is the "Value" of the tire dimension and I see no direct translation to something that could be used as the numerical circumference. For example, when selecting 2260 mm, the "Value" in the UI is 57... this corresponds to hex values for index 100,101(decimal) of block 5.

It seems to be recorded twice. I would guess block 4 is some simple checksum. Subtracting 0xfc18 from the value in block 4 yields the exact same number as that recorded in positions 100,101 of block 5.

Markdown (GitHub flavored):
| Tire Circumference | Block 4 HEX | Block 5 hex digits 100,101(decimal) |
|--------------------|-------------|----------------------------|
| 1760               | FC98        | 80                         |
| 1875               | FCBB        | A3                         |
| 2160               | FC4F        | 37                         |
| 2255               | FC6E        | 56                         |
| 2260               | FC6F        | 57                         |
| 1930               | FC70        | 58                         |
| not configured     | 0           | 0                          |
Even more unfortunately these values don't seem to be in any generalized order. For example value 0x57 (2260mm) preceeds value 0x58 (1930mm). So, it's not like simply putting a larger hex value here will be likely to produce a desired result. My strong feeling is these hex values are looked up and interpreted by some other system.

Two years ago, there was another thread where @ShadeTreeMech had some links to the FORScan forum and even a Google worksheet where Mustang/F150 owners were computing a hex value that could be written to some other area of memory. I wonder if independent of any changes to this new/expanded BCM tire dimension setting there is some other memory value to be discovered and we might make more progress by going that route. Clearly some system is interpreting these hex values and translating them to their circumference equivalents.

Or I am not dumping enough information and there are other changes being made to the vehicle when altering the tire dimension setting. I am new to FORScan so if there's some other way to get more info about changes I am making I could use some help. Any thoughts appreciated.
 

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In case you are a visual learner like me, here is a highlight of the changes between 2260 (0x57) on the left and "not configured" (0x00) on the right.

Are there any other changes being made to my system than the ones I can change in this .cct file?
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