tow haul

[whacked]

I had to pull a pretty heavy trailer today and went to push my tow haul button and nothing happened put it on another truck and his worked so its not in the trailer. Any ideas where to start looking checked the fuses that I thought might be associated with the mode but not sure if I got them all. Hopefully you guys can steer me in the right direction. Took it to the dealer and its off warranty of course. It's a 04 GMC duramax with a allisson.

Thanks

[DmaxMaverick]

There is a known, although rare, cause for your symptom. The wire harness in the column can have broken wire strands within the harness. The repair is a replacement of the harness, IIRC. If you locate a broken strand, I imagine you could splice it if it is in a reasonable location.

[Mark Rinker]

The main thing you'll be missing is the grade braking feature - which really helps with stopping heavy loads, even on level surfaces.

As for the shift points and converter lockup differences, you won't notice much difference in cool weather. In the summer, towing heavy with T/H off will result in slightly higher trans temps.

[JohnC]

Sometimes I can push mine until I'm blue in the face and nothing happens. Wait 2 minutes and try again and it works 10 times out of 10. go figure...

I think the switch must be flakey. Once it works it seems to keep working for the duration of the trip. I wouldn't cancel if it doesn't work.