Just bought my 2000 yesterday. Didn't get a chance to drive it til today because the wife likes it too. But it has 225/70/15 tires on it. Spec is 215/75/15. As a result the speedo is 5 slow. Can a mechanic change the parameters in the computer to adjust the speedo for tire size? Or do I just live with it til the tires wear out? They are at about 3/4 tread life left.

 

You have some other problem - those tires are within 1% of each other. And at what speed does the speedometer display 5 under?

If it's a constant 5 under (i.e., shows 20 at 25, 30 at 35, 40 at 45), the needle has been tweaked and needs to be tweaked back.

RwP

 

How do you tweek it? Its electronic from what i see no cables and the tuners i tried don't have the option on our truck.. whats missing?

 

Try this. There are little marks on the side of the speedometer that it should point to during a self test.

With the key off, press and hold the trip reset button in. Continue holding it and turn the key ON (don't start the truck). Continue holding until CHEC shows in the odometer window. The gauges will sweep - to the marks, and it will test the lights too.

If the needle is off, carefully pry it off and reinstall it.

The other possibility is that somebody swapped out your CAB (controller - anti-lock brake.) It needs to be programmed - with a DRB at your dealer.

 

Talked to a wrench at our local dealer today. He said that can change the programming for about $100. We like the looks of the tires on the truck, so we will probably go that route.

 

It should be an easy fix. Why you need to have it done though is the real question.

 

I say the same just live with it knowing its off a small amount