swapped a 06 4l80e into my 2008 sierra. using e38 ecm and t42 tcm from a 08 6.0 van. tow haul button isn't working now. tried grounding the cable that goes to bcm to activate tow haul and still no luck, tested tow haul button with multimeter and all is good. was looking at some diagrams and seems like the van bcm sends a class 2 data signal to activate tow haul and on the trucks, it's a gmlan signal. not sure if that has anything to do with why it isn't working. any help is appreciated, thanks! oh btw, truck shifts fine, works flawlessly, harness was modified and everything. thanks once again

 

anyone else had this issue?

 

I wish the tow/haul not working was all I had to worry about. My had been stuck in 2nd for two months now. I also wish I had an answer for you.

What wiring mods did you perform for your swap? You said you are literally running a 2008 van tcm and ecm now, or you tuned your factory one to van specs?

 

i followed a tut on here for modding the harness. adding the speed sensor connector, swapping pins etc. i'm running a 08 6.0 van tcm with a 08 silverado ecm. tranny shifts fine and everyhting speedo works. but tow haul doesn't work.

 

bump..

 

bump...tow haul lights up on dash but tranny doesn't downshift or do anything. anyone know anything? thanks....

 

so went to my tuner... he says that the tow haul tables are being accessed when tow haul is pressed. it's just not downshifting? not sure what's going on or why it's not downshifting as its supposed to with the tow haul any help?

 

What downshifting are you referring to?

 

like when you engage tow haul, the trucks supposed to downshift. it doesn't in my case.

 

When you are braking like an Allison?