I have an 05 gmc sierra 1500 truck. A week or so ago my abs light came on as well as my service brake light and my abs was kicking in. Shortly after my speedometer fully stopped working and I was stuck in first gear.

After doing some research I figured out it could be a bad Vehicle speed sensor, on my truck there are two of them in the transfer case and they supply the info needed for the speedometer and for the ecm to know when to shift, they also serve as the abs wheel speed sensors for both back wheels, there are abs speed sensors up front but they only supply info for the front wheel abs system and have nothing to do with the speedometer.

So today I replaced one of the two sensors as when I ordered the part I didn’t realize there was two. After installing the new sensor my abs light went off and my Speedo started to work again but only after around 6 or 7 mph, with it reading 0 going 6 or less. Also too even though my abs light went out my abs still kicks in when slowing down, again once the truck is going less than 7 mph it kicks in. As a result I pulled the abs fuse disabling the whole system.

So my issue is partially fixed but what else could be causing the dead speedometer below 7mph and abs kicking in. Change the other sensor out or look at the front wheel ones? Or is this just a liveable Quirk of the truck for now on? Sorry for the long post