Engine/Transmission (1998.5 - 2002) Speedo 15+ mph off compared to GPS, what gives!

[KCraft]

I bought a 2000 2500 4x4 5 spd yesterday as I'm driving home I notice the speedo is way off, like 15+ mph I compared it to my GPS the truck has 285-75-16 for tires. The cluster?
My cruise don't work either, I was wondering if those could be one in the same

 

[SAndreasen]

285 75 16 tires will throw the speedometer off quite a ways thats the same size both of my trucks run and the speddometer aer both way off you need to find somebody with a hypertech programmer to change the tire size in the computer of the truck a smarty programmer will also do it .

 

[Road Dog]

285/75R16 may put it off a little. It depends on the original tire (it's listed on the door jamb). It should be off by 3-5%, not 15mph. The speedo is driven off the ABS sensor on the rear diff. Is the speedo erratic? Does it move up smoothly from zero? Is the ABS light on?

The speedo calibration is set in the PCM by tire size or revolutions per mile. A dealer can set it but they'll charge you.

 

[SAndreasen]

At 55 on my speedometer I'm really doing just under 65 its farther off the faster you drive at 35 its almost dead on

 

[pgleavitt]

At 55 on my speedometer I'm really doing just under 65 its farther off the faster you drive at 35 its almost dead on

Bought a truck from P.O. that had put 17" wheels and 35x12.5 tires and my speedo did exactly the same as yours. 30 mph dead on and by 55 mph I would be doing just under 70 mph. took it to a dealer and 30 minutes and around $80.00 later it's dead on. Now to figure out exactly how many miles the truck really has on it.

 

[SAndreasen]

I wish I could find a dealer to do it . I'm just goina brake down and get another hypertech programmer

 

[Bob4x4]

I wish I could find a dealer to do it . I'm just goina brake down and get another hypertech programmer

Go to your tire mfgs web site get the revs per mile number for the tire,take that info to your dealer and tell them to go to the abs module to reset the spec or stop by my house lol