AWD Fault after adjusting tire diameter

[OleKennyRoy]

I did a wheel tire change a while back and had the dealer install the tires. I had 225/60R18 and went to 235/65R17. The speedo was right with the OE wheel/tire combo, but was 1 MPH slow with the new set.

I went into the BCM and adjusted the diameter and now I have an AWD Fault.

Has anyone worked this out?

'23 Lariat AWD

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[Jtitzer56]

It happens every time you change it. I can't remember for sure but I think you run the AWD module initialization/relearn from central configuration. If you're using forscan to change it, look at the DTC and I'm pretty sure it tells you what to do to fix it.

 

[Pyro_Raptor841]

That fact that manufacturers continue to fail at implementing basic features like resetting/recalibrating for different size tires is completely absurd. Especially on AWD makes.

 

[Sig-vicious]

I'm by no means an expert on this but I thought I read that there is a maximum value you can set the BCM tire diameter to, and that limit was kinda based on what the max diameter of the stock options were. It would let you save any number you want to in there, but would raise a fault if you exceeded a certain limit. Are you still within the diameter of the factory's largest tire?

Anywho, just regurgitating what I think I read elsewhere here, if you want to do some searching for it. Good luck, I was hoping to step up my next set of tires on my Tremor a wee bit, so I've got some investment of curiosity. Worst case I could live with an mph or two difference if need be. But I like the idea of dialing it in if ya can.

 

[BeardedMarine]

I had the same issue and found no fix. I think the only way to change the tire size is with a tune

 

[Bil13h]

The calibration, as it was explained to me, is never supposed to be exact. There is a threshold spec that they have to build within, and personally, my FWD Hybrid was always off with the OEM tires. I went from 225/65/R17 to 235, and now I am within 1km/hr as the radars and google.

I do understand this is an entirely different platform, but that shouldn't matter for legally required specifications and the tolerances afforded to them

 

[paneubert]

To each their own, but I decided to just not mess with it on mine. My speedometer is always within 1 MPH from the "your speed is" signs on the side of the road. Not enough of a variance to make me care.

I went from 225/65R17 to 245/65R17.

 

[OleKennyRoy]

Clearing the fault isn't actually that big of a deal... There is an option in Forscan. I unfortunately realized that after resetting my PCM. Truck is now at the dealer because I don't know how to make it recognize the VIN, and my Googlefoo didn't find any results...

 

[Montana]

That fact that manufacturers continue to fail at implementing basic features like resetting/recalibrating for different size tires is completely absurd. Especially on AWD makes.

This is not a manufacturer issue nor is it a basic issue. Hell, it's not even an issue for most people going up a size or two. Being off by 1mph for aesthetics isn't that serious.

 

[BeardedMarine]

Mine is off by 3mph on factory sized tires.

 

[Bil13h]

Mine was too, and then I went up to 235s and now it's 1km off

There's a regulated tolerance, and it exists beyond any calibration setting

 

[AzureBlueBill]

Why bother messing with it? Factory speedometers, and odometers are not known for their accuracy anyway. At a possible 1% deviation from what you think it is supposed to be, it's entirely possible you actually made it more accurate. Or not. Mine is in theory off 3%. Just remember you are going a tiny bit faster than the speedometer shows and all is well.

 

[OleKennyRoy]

Why even have a Forscan forum? Why even have color choices? Why? Because I wanted to, and successfully did.

I just so happened to make a change I was unable to fix because I couldn’t find good instructions for the AWD relearn.

I did the math to calculate the difference I saw vs the value entered, then verified using two different GPS speedometers. I then fine tuned and got it within 1/2 MPH.

 

[Beamcrazy]

Why even have a Forscan forum? Why even have color choices? Why? Because I wanted to, and successfully did.

I just so happened to make a change I was unable to fix because I couldn’t find good instructions for the AWD relearn.

I did the math to calculate the difference I saw vs the value entered, then verified using two different GPS speedometers. I then fine tuned and got it within 1/2 MPH.

Ever come up on the relearn? I just accidentally did the same thing, it's snowing now and I have to commute home, so i suppose we will find out if the AWD system works and is just complaining, or if we really have problems.

I wont be resetting any modules, or loading up my factory AB.

If you find anything out from ford on how to do the relearn, please drop a line.

Good luck getting your truck back

 

[Beamcrazy]

It happens every time you change it. I can't remember for sure but I think you run the AWD module initialization/relearn from central configuration. If you're using forscan to change it, look at the DTC and I'm pretty sure it tells you what to do to fix it.

It does not, unfortunately. I can't get it to say any relevant info on what the problem even is, and how to fix it.

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