From some quick google searching, you may need to get a HP Tuner to change the max tire size limit in the PCM

How to use FORScan to adjust tire size - Page 6 - FORScan forum

 

I guess I will finally have to figure out Forscan. Thanks for doing the work on this! While being 10% off on the speedo doesn't bug me, being off on the odo does. Please let us know about the ABS code.

 

why does it bother you more to be off on the odo?

 

^^^ I drive about 5,000 miles a month in my van, so 5,000+10% = 5,500. Over the life of my van (probably 150,000 miles), that's a difference of 15,000 miles. The van's computer would think it traveled 150,000 miles, but it actually covered 165,000 with the oversized tires.

 

FWIW, even with the ODO out of calibration, the driveline components will have only rotated the equivalent of 150,000 miles and it's this that matters most from a wear perspective.
I'm pretty sure the Transit's speedo and ODO calibrations are locked because our vehicles are primarily parcel vans and DOT doesn't want anybody screwing around with a commercial vehicle's driven mileage. It's regulatory driven.

 

Were you ever able to clear the ABS fault code?

 

Were you ever able to clear the ABS fault code?

So far no. It seems to do with wheel revolutions not jiving with the range of what the computer wants to see.
Troubleshooting it is on the back burner for now since it involves making changes, clearing codes, and then test driving each time.

 

Newbie here, does foreskin...I mean Forscan effect factory warranty?

 

Only if it cut of by an unlicensed practitioner.

Would probably depend on the dealer and what you used the tool to do.
If you want to read up on the letter of the law, it's called the Magnuson - Moss Act. Of course in a practical sense ...^

 

( redacted )

 

 

I must be missing something. How do you get to the Central Configuration? I have the Body Control Module, but no Central Config.

Forscan 2.4.8, advance key

2021 Transit 350 DRW 3.5 ecoboost

245/75/16

 

I've not gotten my hands on a post-2020 model to explore yet, some of the menus and parameters are likely different.
This is where it is when connected to a 2015:

 

Any updates? Has anyone been able to run larger tires with an accurate speedometer and not throwing a code?

 

I haven't had any luck yet.

 

Thank you both for the update. Hopefully those are all warnings that you can safely ignore 😁

 

UPDATE NOT SUCCESSFUL AFTERALL SEE NEW COMMENT****

Well I'm not the OP but I do have a bit of an update on speedometer calibrating with forscan. I added some 245/75/r16 Falken Wildpeaks and gave forscan a shot to recalibrate my 2020 AWD/Ecoboost transit, fully expecting to replicate the results seen here and have a christmas tree on the dash but a calibrated speedometer. The results however ended up being far better than expected! I do still have one error--A U0422 PCM error, which is apparently the PCM being mad about the size being out of the anticipated range--but it is not an error that leaves a visible dash light! Immediately after writing the new tire size the van had an AWD fault and a P160A error code. I first tried running a PCM relearn, which did not work, however after running the AWD system relearn and another PCM relearn all I was left with was the U0422 and no dash lights! A quick google suggests U0422 is common issue and likely easily fixed by a shop with the right tuning equipment or an HP tuner, like mentioned earlier in this thread. Here's a screenshot from forscan showing the AWD relearn option I ran:

I'm not sure if these module relearns have been available for others in the past but they were today for my van! A test drive 30 minutes ago verified that the speedometer was correct (1 mph high vs gps speed at 30-40 mph), which I am a-okay with for now. Tomorrow morning I'm going to test the odometer readings on the way to work to verify that it is indeed correct or at least close enough to correct to live with as well as a highway speed gps speed check. I'm anticipating some fine tuning to get it bang on accurate, but in the mean time getting this fixed has my stoke level quite high!

 

Fantastic. Sounds like the computer changes that came in 2020 are on your side.

 

Well sadly I seem to have spoke too soon. The highway test did not pass, and my speedo/odo are still running ~8% under actual speed. It's a tiny bit better, and while I can't verify it the shift points do feel a bit better, but the speedometer is sadly NOT calibrated. Back to the drawing board!

 

Given that Ford is putting 245/75-16 tires on the upcoming Transit Trail model I'm hopeful we may finally have a better way to tell the vehicle we're running larger tires 🤞

 

Edit: Stoked the trail has the larger tires. Hopefully we can use the trail as built data on the normal 2020-2023 AWD vans.

 

Confirmed that a simple Tire Circumference change in a 2023 AWD Transit does nothing to change the speedometer, but DOES throw a code in the AWD system.

 

Someday we will get someone to dump the Transit Trail config...

 

I have recently acquired the HP Tuner OBD unit and software and there is a Speedometer calibration configurator.

The tuner guy said be careful with it.

There are many different sections that allow alterations but I am a bit scared to try it.

Obviously I can take take all of the stock settings and change back at a later date but I'll probably ask HP Tuner about it first before messing with it.

You can input final gearing plus tire circumference and more.

Edit: max tire circumference is 2536mm which is very close to my 31.8" tires.

Just so I don't brick anything I'll put the email to HP Tuner first.

 

This looks promising:

"Thank you for contacting HPT Support.
You will not be able to use that, but if you read out the stock file from the editor program you should see a tab marked SPEEDO, you will make the changes under that tab."

 

I have some good news. The dealer that just flashed my ECU back to stock(after the tuner guy got it way out of whack) said they can adjust for tire size at the dealership now.

They didn't have enough time to tackle mine today. The next time I'm in Utah I may schedule an appointment if I don't figure it out directly with the HP Tuner flashing software.

 

I tried doing the tire size and gearing correction and thought it worked initially but it may have been the gps still picking up satellites.

Next step is to ask HP Tuner again how exactly and or take it to the dealer.

 

Got a reply back from HP Tuners. I'll be using the beta version of their editor and doing the same steps again and it should work.

Updates this evening when I get home.

 

The HP Tuner beta software did not do the trick for the speedo. I can tell the gearing change worked though as it shifts better now without lagging down in power.

Put another email to HP Tuner to see what they say.

It is very tempting to drive up to Cedar City tomorrow to see what they can do.

I'd hate to drive there just for them to not be able to do it so next week when I have to be there for work will be a better proposition.

 

I’m very suspicious of the dealer being able to do anything. Unless they’ve said they’ve done it before on a Transit specifically.

many have tried and failed to do this through Forscan or dealerships

 

At this point, I am suspicious as well. Next week I'll give the dealer a go again while I'm there. Can't use local dealers as they try and charge several hundred dollars for a few minute flash.

The dealer I will be using said it is more involved than just an ECU flash.

 

HP Tuners is willing to look into the issue but I'm taking the lazy route first and going back to the dealer that said they could do the change.

Fingers crossed. Updates tomorrow.