I know I've seen some thread on here before but for some reason can't find it. Anyways, I have a 2012 F-250 XLT with 3.31's and 275/65/18's. I know the 20 inch wheel wasn't an option with the 3.31 on the XLT's but there is a guy locally selling his factory 275/65/20's. If i go the bigger wheel/tire will it throw the CEL?? I thought I read something about there is a way the dealer can fix it but I can't remember for sure. Thanks a lot.

Wes

 

The dealer can update the CPU with a new tire size, but if your CPU is set for a 3.31 rear axle the software won't let the dealer input a 20" wheel. They'll have to play with different tire sizes on 18" rims to get close to what your actual diameter is with your 20" wheels. Sounds like some dealers aren't willing to fiddle with it like this, though.

 

Or get a tuner and be able to set it wherever you like up to 34.10" which is a 35" tire.

 

I had the same issue. I haven't heard of any dealers that are not willing to reprogram. The largest 18" wheel size that they can select is 275/70/18. (what my dealer told me). Any 20" selection with throw a CEL.

 

Does anyone know if I go from 20's to 18's will it cause a CEL.I plan on going with a 35 and find more options with 18" than with 20's.

 

First, this is only an issue if you have 3.31 gears. You must have 3.55 if you have stock 20".

Second, you can put whatever tire you like on the truck, it does not know what is physically on there. The problem and what will throw a CEL (again, 3.31 gears) is when the dealership tries to reprogram for that size to calibrate the speedometer. The only way to get to a 35" tire size is to select one of the 20" wheel sizes. Since 20" wheels were not available from the factory with the 3.31 axle it will cause a CEL.

The largest 18" selection is 275/70/18 which is a 33" tire.

To answer your question.....no.