My new jku has 730 miles on it, about 350 in its current form. This morning the check engine light came on. I am doing gears in a couple weeks so I thought I would buy the procal then but I'm thinking maybe the tires are throwing the code? Going to get the code at lunch, just thought I'd get some input. I know changing gears without procal will throw code so I would assume a big tire change stock 225-75 16's to a full 35/12.50.

Any thoughts?

 

Tires won't make light come on. I'm running 37's with no adjustment and mine is fine. Only thing bigger tires will effect is your speedo. Mine is right at 6 mph's below the speed I'm actually traveling

 

Hmm... that sucks. I was hoping it could be that simple. I'll get the code in about 30 min.

So how does the computer sense a gear ratio change and trigger a code but not trigger based off the addition of larger tires? odd

 

The computer has information coming to it through the VSS (speed pulse signal) and compares that to the RPM. I don't see how it could cause a code for either since all changes in ratio, tire size or gear ratio, would occur after the tach signal and the transmission VSS signal. Unless it is actually comparing those with ABS wheel speed sensors on each wheel as well. Then, maybe, it would have the ability to "see" a difference at each wheel that might cause a code. Bigger tires would cause slower axle revs for a given speed pulse and rpm. Maybe. Don't know for sure.