I have a 2000 blazer, 2dr, 4x4. My speedometer (50)is reading about 4 or 5 mph faster than a GPS (45-46)app shows.

Tires are standard for this truck, 235/75R15.
Help please.

 

A dealer might be able to reprogram the computer (ECU or BCM) so that it is calibrated correctly. I was looking at an OBD reader that I think, if I read the specs correctly, could do this too. (https://www.videntstore.com/wholesal...scan-tool.html)

 

I think it's fairly common for speedometers to read a little bit fast. Maybe not that much, though. Personally, I would probably "correct" the problem by replacing the tires (when they're worn) with the next size bigger. You might also find some that are the same size but actually measure larger. Check out the specs for revolutions per mile. Most tire manufacturers provide this.

 

Last I remember, recent history, it had been accurate. Theres been no tire change or issues.

 

That's odd, for sure. If you have a scanner, maybe check the speed sensor output to see if it matches the gauge? Could be that the speedometer itself is not reading accurately. Just a WAG, though.

 

I replaced my tires. I'll get back to this post when I can see if it makes a difference. Currently getting my fuel pump replaced.