what's up guys I have a 2004 sierra 2500hd 6.0 with a 4L80e tranny, same thing as a chevy haha. It's throwing the code P0502 (vehicle speed sensor low input) I changed both speed sensors, 1 on the transmission, 1 on the transfer case, problem is still there. Changed the fluid and filter too. Also has abs light saying all 3 abs sensors circuit malfunction, and service brake system light is on. It's shifting really hard, it's in fail safe boosting line pressure to max. Just wondering if anyone has had a similar problem. It shifts smooth in 4wd though, shifts hard in 2wd and shifts too early.

 

the code is for the output speed sensor...which is the one on the tcase
at this point check the continuity of the wiring from the pcm to the sensor.
-key off, unplug the speed sensor and pcm connectors (conncector c2 pin 20 green black and pin 21 purple white wire
-ohm check the wiring for high resistance, opens, short to grd

 

Thanks for the reply, even though it’s a year later. I was able to fix that problem but now a year later the code is back as well as the symptoms. If all sensors are new and wiring is intact, is it a possible there is a mechanical problem with the transmission?