Copy that nogo, I was going off what I had read on this forum about where the speedo picked up its signal, but in the end it was the water in the GEM that was causing all the havoc. Now just trying to find where the water is coming from.

 

The usual culprit is a leaking windshield. The location of the GEM is prone to trap water if the windshield seal is leaking.

The VSS and ABS sensor for the rear axle are the same part, located on the differential housing. The transmission has TSS (Turbine Shaft Speed) and OSS (Output Shaft Speed) sensors. (Assuming 4R100 transmissions....)

 

Thanks shake-n-bake for the info on the sensor. Pretty sure it is the windshield, after washing the truck today found a drip on the "A" pillar, I left the plastic off so I could monitor. After spraying upper right windshield I could get water along edge of window seal and it then travels down to "A" pillar where it looks like it travels down between 2 pieces of steel that make up "A" pillar and then seeps out the bottom of "A" pillar, which in turns puts the water straight above the GEM, it first drips down onto the small defroster tube leading to left side of dash for window. From there it can drip down and find its way to GEM module, I think A little more verification and will be ready to bring in the glass man for a reseal.

 

Had the windsheild replaced, there was very little sealant on top left of windshield from factory. Glass guy said it was one of the worst he had seen from factory. Feel confident about fix.

 

Hay any luck with your excursion im having the same problem with my speado mph not working abs light on od light flashing but runs fine just changed the vss and nothing happen oh I have a 2003 excursion 5.4 v8

 

If the new VSS didn't fix it the problem is probably in the wiring to the VSS.