When starting my 2000 Blazer the other day, for the first 200 feet of driving, the ABS light never went off, the speedometer remained at 0, and the transmission wouldn't automatically shift. Within 60 seconds the light went off, the speedometer started working, and the car shifted. It has done this two other times since but always behaves normally within a couple of minutes. I don't see how all three of those systems could have failed especially since they all work properly the rest of the time.

(I recently did some work in a couple of different areas but I'm curious how people will respond without further details. I don't want to unduly influence anyone's opinion especially since the work might not have anything to do with my current problem.)

Thanks.

Jack

 

All three of those systems have at least one thing in common, the VSS (vehicle speed sensor). Something is causing an interruption in the signal from the VSS to the PCM, resulting in the symptoms you are experiencing.

This OBD2 trouble code thread has the wiring schematic:
P0502 - VSS (vehicle speed sensor) Low Input

 

I too think an electrical connector that is loose. That happened to our fuel pump when the crankshaft position sensor connector got loose.

 

Thanks to you both! I just had some work done and although I haven't crawled underneath it yet to figure out where the VSS is located, I'm wondering if it was somehow damaged when the rear main seal was replaced. (cheap part, a lot of labor!) Seems too much of a coincidence, but then again, I'm not sure where these two things are in relation to each other - yet.

Jack

 

swrtlkk - thank you. I replaced the VSS and that did the trick. Part cost about 60 bucks and it took longer to take off the skid plate than it did to replace the part - super easy. I'll try to attach photos to this post in the hopes that it helps someone else.

Blazer Forum - Chevy Blazer Forums - barredjack's Album: Vehicle Speed Sensor

Jack

 

I am glad that my information made for a quick & easy fix for you! Thanks for letting us know!

 

I have had this exact problem in the past but at one point it went away and I didn't wind up changing the VSS, which I imagined was the case.

How much did this affect your transmission when you were having this issue, did the truck go into limp mode/rumble when stopped at a red light/flashing check engine light?

 

flashing check engine light means servere misfire. Its probably in limp mode because of that.