alright here's the run down 2001 superduty with the 7.3L auto transmission. Driving down the road yesterday the speedometer starts bouncing... It's raining and cold. the O/d off light is blinking on and off. I've got a waste gate code a p0500 VSS Sensor code and a insuffecient fuel pressure code. the waste gate and fuel pressure are from my chip i know that. i get home get on fte and search for a solution.. I've come up with two possibilities. the differential sensor or the GEM. Without just throwing parts at it is there a way to check this and find out where the problem is coming from?


p.s. I have the edge monitor and it won't show torque readings or speed

 

If you have a scan tool or some sort of way to monitor data stream. Replace the VSS on the rear differential. I've replaced 100's if not 1000's. They are cheap.

I've never seen or heard of a GEM causing this issue.

The only other thing I've seen cause it is the instrument cluster. But it's rare.

 

Ok guess we'll start there tomorrow

 

I agree. Its not uncommon for the VSS to break.

 

And now today the speedo is working fine without changing the sensor???

 

it can be as simple as just rewrapping / sealing the connection to the VSS. happening when wet is a classic sign of this.

 

My 2000 F450 is doing the same thing, one start it doesn't work, the next is does- mine is all or nothing, perfect function or none at all.
I'll be picking up a sensor the next parts run.