Speed Issues

[username333]

I have an Issue with my speedometer. The speed not only reads faster than it should, but it reads faster and faster the more I pick up speed. example- 45mph is read at 50mph, 70mph is read at 80mph. Im wondering if my issue is a speed sensor along with needing to calibrate for my bigger tires? the same issue occured with factory recommended tire size.

 

[DerekTheGreat]

We need to know what year your truck is for proper diagnosis, but the sensor either works or it doesn't. However, the DRAC module is responsible for converting the sensor's input into the speedometer's reading. Wild guess, you've got a 1988-1991 truck that someone swapped the instrument cluster out on.

 

[SomeTahoe]

What gears did your truck come with/have now? I was thrown off by a similar situation, turned out PO changed stock 3.73 gears for 4.10.

 

[Onizukachan]

Sounds like you are a percentage off, not a fixed amount off.

and it sounds like possibly shorter tires, shorter rear gear, etc and not an actually fault or failure anywhere Since it is pretty close to Speedo is 10% higher than ground speed.