I moved my fuse box and ecm behind my front bumper and have been having issues with the wiring. I read somewhere that you can not add any length of wire to GMLAN wiring. Any one know if this is correct and what issues it may cause? I of course extended these wires.

 

You can add wire, it just needs to be twisted like the stock wiring is.

 

That's interesting. Wonder what effect the twisting has. Do you think not having the gmlan wires twisted could be the reason I have no power to pin 50 at the ECM which is fuel pump signal?

 

Could be the reason, yes. Twisting prevents crosstalk on paired data wires. If they aren't twisted it is likely interrupting communication between modules on each side of the non-twisted section. Pull back the loom on the OE harness, you'll see what I mean. Try to match the twist rate from the stock harness when you fix it.

 

Thanks for the advice hopefully I did not F it up to bad. There are a lot of twisted wires. I will need to find a schematic of the gmlan wires to make sure I get all of them.

 

Looks like I have to sets of brown and brown/tan wires coming from the rear of the truck on set goes to the ECM high speed gmlan wires. The other set goes to the x109 connector. Anyone no where these end up on the other end? Wondering if I mixed them up.

 

They are parallel connections, so it shouldn't matter if you mixed them up. What happens on the tan wire at the FPCM also happens on the tan wire at the ECM.

 

smokeshow your a lifesaver I twisted the 2 sets of tan and tan/black ( for some reason put brown in the previous post) wires and now have power to my fuel pump. Do you by chance know how many sets of gmlan wires there are I want to make sure I find them all and get them fixed. Been fighting this problem for almost 2 weeks now. I'm sure there will be more but I'm getting there. Thanks for helping.

 

If you only moved the ECM, you only affected that pair. Since its a parallel connection, it just bounces from module to module...there's no dedicated connection from the ECM to TCM or ECM to BCM, etc. Just fix the one you changed.

 

I moved the fuse box as well so every connector under the hood was moved to behind the bumper. I'll just unloom everything and check for twisted wires. I only have a couple more mysteries 3 purple/white wires going to the back of the truck I need to find where they start and end . I need to check continuity and make sure they are connected correctly before I try and start the truck for the first time.