No Speedo, No shift, VSS good

[James Daniel Munns]

 

Ok so this is the weirdest and tbh most frustrating issue I’ve ever dealt with. My TEHCM needed replaced so I ordered a warrantied rebuilt one. Thanks solenoids for failing. Anyway, I got it installed and now....the speedometer stays at zero. And the truck stays in first. So far I have:

flashed the tcm using GM SDS
updated all modules to current using GM SDS

Mind you I was driving this truck every day before I swapped out the valvebody/TEHCM. So the VSS isn’t bad. On the topic of the VSS. When I watch live data in GDS2, the vehicle speed rapidly fluctuates between 10mph and 250+ mph. Also, when driving I can use GDS2 to manually command a shift to second gear successfully. 3-6 I can command, however it isn’t shifting and I assume it’s because of the speed. I’m at a loss on this. All modules show they have the most current software installed, and the correct vin written to them.

vehicle is throwing no codes at all

[James Daniel Munns]

SOLVED:

 

ok for anyone scratching their head on this one. The problem was buried very deep in the truck. Specifically between the transmission valvebody and it’s mating surface. There are 2 sensors on the top side of the valve body. Looks like my new valve body has bad sensors on it!!! Would have been nice to know that before spending $180 in transmission fluid. Lol 

according to the wiring diagram, the VSS circuit passes through these on its way to the ECU. With them being faulty, it explains the erratic readings in GDS2, the no shift, and the no speedometer read out. 

 

[silveradosid]

thanks for the follow up. just a question but didnt gds2 show a faulty signal from the sensors. i have gds2 and was wondering

[James Daniel Munns]

Interestingly enough no. It never coded the VSS, however it was showing unstable data coming from the VSS. Speeds ranging from single to triple digits. I’m guessing this aids the TCM and ECM in doing what the older chevys did with a speedo buffer. Since the VSS is a Hall effect, I’m guessing as long as something is coming from it, then the ECM assumes it’s good.