Speed Sensor location?

[cdig]

Can anyone tell me where to find the vehicle speed sensor on my 04 GMC Sierra 2500HD? 4L80e trans... I have no speedo and the ABS and emergency brake lights are on. Trans also shifts really hard most of the time, and readin on the forums seems to point to the speed sensor but i can't find anywhere that gives the location! is it that sensor on the upper driver side of the tcase?

Any other ideas on possible causes for these conditions?

[clinebarger]

Originally Posted by cdig

Can anyone tell me where to find the vehicle speed sensor on my 04 GMC Sierra 2500HD? 4L80e trans... I have no speedo and the ABS and emergency brake lights are on. Trans also shifts really hard most of the time, and readin on the forums seems to point to the speed sensor but i can't find anywhere that gives the location! is it that sensor on the upper driver side of the tcase?

Any other ideas on possible causes for these conditions?

Heres a diagram, It can also be a wiring problem

[cdig]

Actually fixed it tonight! I changed the speed sensor out for a used one I had and the dash lights stayed on even after clearing the codes. I buffed up the ground wires on the frame under the drivers door and disconnected the battery. Abs and ebrake lights stayed on until I had it backed out of the shop, then they suddenly went out! Trans shifts are much nicer now, speedo works again... So I'm not sure if it was the bad grounds or the speed sensor but it's fixed now!

One thing I did notice on the test drive is that pushing the tow/haul button didn't seem to change the shifting. It's hard to tell if it's actually going into OD though. Does 2200rpm at 60mph(100km/h) sound like its still in 4th? Or is it in Od and my tow/haul switch is t doing anything? The dash light comes on but it doesnt downshift when I turn it on at hwy speed.
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[cdig]

Btw, thanks for the diagram! Much appreciated.
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