Got an 01 cummins 5 speed manual. Have superchip flash paq on fuel saver mode other then that everything is stock. I keep getting dtc p0500 and p1693. Which I know is a speed sensor and a fault in companion module. So here's the weird part. I replaced the speed sensor on the rear diff, yet the truck is still limited to 55mph. Throttle completely drops off once this speed is reached. So I unplugged the speed sensor and the truck runs fine, but the speedo doesent work and I have a brake light and abs light on. If anyone knows anything about this please let me know.

 

I do know that the rear speed sensor is also the ABS sensor for the rear anti lock brakes that would be why the ABS light comes on. There is a trigger finger on the ring gear that makes the signal to the sensor. It could have some gasket sealer or foreign object it picked up on it and is causing a false signal. Might be worth pulling the rear cover to check.
Other than that the problems sounds electrical. Did you clear the codes after the new sensor was put in? did the code come back?

 

I pulled the cover off already to check and nothing out of the ordinary. And yes all codes were cleared when I put the new sensor in.

 

also I only get the abs and brake light when I unplug the rear speed sensor. When it's plugged in everything works the truck just won't run over 55

 

Have you done any recent maintenance besides whats listed?

Do you have any other Mod's? turbo, FP, injectors, ect.

If the truck is still throwing codes for abs and companion module I would take a close look at all you connections and wiring at the ABS controller, sensors, PCM, the VP pump harness if tapped for your programmer.
Fuses inside and out.
I don't have my books with me to trace the schematic at the moment.

 

Started me wondering if you have a clogged fuel filter and the throttle position sensor is wide open with your foot on the floor and the speed sensor is seeing no speed increase at WOT and throwing a code.

 

All stock. It runs fine with the speed sensor unplugged so I don't think it's the filter. I've got 10psi at the vp at idle which will change when I install a fass. I've checked the fuses under the hood and they were all good. I haven't checked the ones in the cab though, I'll do that after work. I've also checked as much of the wiring as I can see.

 

I am not familiar with the programmer you have I see you said that it was in fuel economy mode could the program or chip be at fault? Maybe try disconnecting the programer or chip flash back to stock?
Definitely get the pump upgrade

 

I've set it back to stock still flat lines at 55. It weird it completely loses throttle response. It's gotta be wiring or a computer problem since I can un plug it and the truck will run fine.

 

Any Updates?