Our city has installed some new radar speed signs at each edge of town to show your speed entering the city limits. My '93 CC is right on the money at 30mph.But noticed that my '04 is 4 mph fast. Speedo says 34 mph and sign says 30mph. Can this minor of a difference be adjusted to correct. Don't know if this increases as miles per hour increase.........hate to go thru town at 60 mph to see. If it does increase, odometer will show way more miles than is accually on truck.
Mentioned it to my local dealer shop foreman and he just srugged his shoulders and walked off.

 

Yes you can. It sounds like you may have put bigger tires on the truck. I'm not familiar with the '93's but it should definitiely be possible. Search the forum for speedometer calibration. There's tons of threads that might give you specific info.

 

Iv heard that its as simple as plugging into the PCM on the newer trucks. but im not really sure.

 

I had actually started writing this up one way, but had to delete it all once I really got to thinking about what you'd said. You're saying that the speedometer reads faster than the sign clocks you at?

If that is the case, you would have to be running smaller tires than stock, as smaller tires would have to revolve more times per mile than a set of larger tires.


There is some flexibility in the PCM to compensate for different sized tires. What you will need to do is find the revolutions per mile value for your specific tires (can generally find this value on the tire manufacturer's website or at a tire shop), and then see if you can get the dealer (or helpful friend with a programmer) to program this into your truck. Be forewarned that A.) the dealership will probably charge a minimum of 30 minutes labor for this, and B.) your tires' revolution per mile value may not be within the range acceptable by the computer.

On the upside, correcting this will not only correct your speedometer & odometer readings, but it will also help your ABS system.


Find a different dealer, or go above his head. If he can't spare the time to even give you some assistance, there is absolutely no reason to give them the benefit of your business. Just my two cents.

 

Thanks for the advice

The tires that are on the truck are what came with it new.
LT265/75RX16, these equal the same highte as 235/85RX16. If what you are saying then; if I switch to a 285/85RX16, then the speedo should be more accurate!

thanks again