'01 Sierra 3500 Not Communicating With Scan Tool

iwantoneofthose · January 26, 2010

Hi all,

I recently purchased a '01 Sierra 3500 with the 8.1L BB and Allison trans. Because I am currently in the communistic state of Kahlifornia I need to get it smogged. However, the check engine light is on, but my Mac Tools diagnostic scan tool cannot communicate with the car to read the codes.

After doing some (a LOT) of research on the web and in the (useless for HD models) Haynes manual I traced the wires from the diagnostic link connector to "splice pack 205" (aka SP205). With a diagnostics chart I got off the web for another vehicle with SP205 I took the splice pack apart and made a jumper wire to test what was causing the scanner to not be able to communicate, and it ended up being the yellow wire, which according to this page (bulletin for the NSBU switch) it's the serial data circuit "CKT 2470" wire and it goes to the TCM. I traced this wire in the engine compartment to the mentioned connector C106 by the fuse box all the way to the TCM, and it had continuity the entire way. So...does this mean I need a new TCM? I can read and clear the codes when I jump some of the wires in SP205 but supposedly the smog machine needs to be able to communicate with the OBDII system and retrieve readiness codes...

Does anyone have any ideas or experience with this? My temp permit expires at the end of the month. So far the cats have been replaced, NSBU switch, wires, plugs, fuel/oil/air filters, and all four O2 sensors have been replaced. I'm pretty sure it'll pass the sniffer, but I'm doomed as soon as the DLC is plugged in...

thanks in advance!

Jeff