O7 Dmax your thoughts

[RI Chevy Silveradoman]

My tow haul light comes on whether I have the trailer hooked up or not. The tow haul does provide some braking benefits, but I think it is due to the Allison downshifting at higher shift points and RPM's.
I am with Ferm on the fact that there is a towing relay in the fuse box under the hood that works the trailer wiring harness. Some trucks also came through with the 5th wheel harness that is wrapped up somewhere next to the fuel tank. You can see the 5th wheel wire harness by looking between the small break where the truck and bed meet. Not that it makes much of a difference, but just thought I'd mention it.

 

[Ed HD]

I agree, there are fuses for each of those. Happened to my buddy's dad's 02 Silvy and our 05 Duramax, popped fuses under the hood. Super simple fix.

 

[bison]

I'm pretty sure the trailer power all comes from it's own dedicated circuits i nthe underhood fuse panel. These aint nothin like the old GMT-400's, GM actually put some thought into them and set them up to handle high current loads for large trailers.

I agree, there are fuses for each of those. Happened to my buddy's dad's 02 Silvy and our 05 Duramax, popped fuses under the hood. Super simple fix.

You are both right on the trailer lights having its own fuses,...but they are not (at least in my truck) under the hood.
I found I happen to have 2 sets of fuses in the dash fuse panel, one set for L/R truck signal and next to them are two fuses for the trailer L/R signal.
one of them was popped.:agreed:
Yes,..simple fix ..if one knows of their existence, the fuse lay out on the cover sure didn't list them:rolleyes5:

Anyway the Tow/haul works intermittent,..the light comes on and goes off at will.
I took a 10.000 lb load of bison to the butcher with this truck today,..it sure beats the old 98 in pulling power i tell ye. A 2 ml long grade 7 slope uphill means nothing to this beast:thumbsup:
Going down hill was another story, with the non working tow haul it sure felt i was in mexican overdrive even with the shifter in M and shifting back to second gear i was doing 65 ml/hr with the RPM's pegged at the redline.
I thought this thing had an engine brake?

 

[ak diesel driver]

that woulda been fun to watch LOL

 

[Pepperidge]

You are both right on the trailer lights having its own fuses,...but they are not (at least in my truck) under the hood.
I found I happen to have 2 sets of fuses in the dash fuse panel, one set for L/R truck signal and next to them are two fuses for the trailer L/R signal.
one of them was popped.:agreed:
Yes,..simple fix ..if one knows of their existence, the fuse lay out on the cover sure didn't list them:rolleyes5:

Anyway the Tow/haul works intermittent,..the light comes on and goes off at will.
I took a 10.000 lb load of bison to the butcher with this truck today,..it sure beats the old 98 in pulling power i tell ye. A 2 ml long grade 7 slope uphill means nothing to this beast:thumbsup:
Going down hill was another story, with the non working tow haul it sure felt i was in mexican overdrive even with the shifter in M and shifting back to second gear i was doing 65 ml/hr with the RPM's pegged at the redline.
I thought this thing had an engine brake?

get tow haul working and you will have "grade braking" through the transmission

get someone to program your ECM and you can get a turbo brake programmed into it...which by the way the 2015 Dmax has added...so the variable vane turbo brake must be a good thing if the General decided to add it...

 

[THEFERMANATOR]

The turbo brake can be added to an LBZ by adding in a switch or by a custom tune.

http://www.thetruckstop.us/forum/showthread.php?41591-LBZ-HOW-TO-Activate-factory-turbo-brake

When you say the tow haul works intermittently, does it only work when the light is on? Other than a bad ground somewhere to the BCM, I don't know what else could cause it to work intermittently.

 

[bison]

that woulda been fun to watch LOL

Funny guy you,..i did'nt mean THAT kind of brake :hihi:

The turbo brake can be added to an LBZ by adding in a switch or by a custom tune.

http://www.thetruckstop.us/forum/showthread.php?41591-LBZ-HOW-TO-Activate-factory-turbo-brake

When you say the tow haul works intermittently, does it only work when the light is on? Other than a bad ground somewhere to the BCM, I don't know what else could cause it to work intermittently.

I can't really tell if it it works or not cause the time the light on doesn't last long enough. when the light goes off i have to push the button again to make it come on again,..half the time it doesn't and the other half it doesn't last long before it goes off again.:agreed:

I can take it to the stealer to have them look at it but with their labor rate at $140 an hour i ain't chomping at the bit to go there:nonod:





here is the full article for the turbo brake.

Alright. I've been sitting on this for quite a few years because I had planned on making money on this mod and selling switches and full install instructions, but I've just been dragging my feet too much to make it happen. Now that there are less LBZ's on the road there is probably less demand. So, I'll get on with it.

Download:
Light Duty Elecrical manual (25-3500)
http://www.gmupfitter.com/files/medi...Electrical.pdf

Medium Duty Electrical manual (45-5500)
http://www.gmupfitter.com/files/medi...Electrical.pdf

In the Light Duty manual navigate to section C-14 thru C-15 which are pages 72-73 of the PDF. Take note of pin 11 and 53 of the C2 connector. Notice they say unused.

In the Medium Duty manual navigate to C-21 thru C-22 which are pages 80-81 of the PDF. Take note of pin 11 and 53 of this C2 connector. This manual says:
C2 pin 11 (exhaust brake telltale)
C2 pin 53 (exhaust brake control)

This is the thing that got me to thinking 4 or 5 years ago. We all know that the '06 and '07 MD trucks that have the RPO of LLY are actually packing an LBZ engine with an MD tune of only 280hp, (or something close, or whatever) while the '05.5 - '07 classics have the same setup but have the LD tune of 360hp. So, knowing GM is all about recycling parts, programs, computers and whatever else, I wondered if they left the logic for the Turbine Brake from the MD programs in the LD programs. So, on a hope and a dream I wired up my switch according to the diagram of the '07 MD w/ RPO LLY. Wouldn't you know it actually worked. They did leave the logic for the exhaust brake in the LD ECMs. HOWEVER, the brake only activates while the TCC is locked up, eg. T/H mode activated. Also, with the exhaust brake activated it sends the TCM into a more aggressive down shifting map. Being, what I would refer to as, a power user of EFI Live I also attempted creating a .cax file to add tunability of the brake, but it turns out you need ALOT more knowledge of binary addresses and such that I don't know. I inquired a fellow from NZ who has made cax files before for gasser but he couldn't help me. I inquired with Ross too, but I never got very far with him. He is an extremely busy fellow. Enough history. Here it is. Im not going to tell you how to make a switch, and I'm not going to tell you what the part numbers are for the ECM pins. But I will tell you how it works and what you need to do to get it to work.

The way it works.

When C2 pin 53 is grounded this arms the exhaust brake. When all conditions are met the brake will activate. (vanes close to 100%) When the exhaust brake is actively braking pin 11 of C2 is activated sending 12v to a lamp if you choose. IT IS IMPORTANT to use an incandescent lamp and NOT an LED to act as the telltale. I originally used an LED as my lamp and it was causing some sort of fault with that subsystem making the brake engage and disengage rapidly, switched out to an incandescent lamp and it solved the problem.

Quick FAQ:

Q. Do I have to have EFI Live to make this work?
A. Nope. This is a factory loaded feature. However, EFI guys will love being about to have 5 tunes with and without the turbine brake instead of making one tune with the brake and 4 tunes without.

Q. Will this work on my LBZ/ Bosch controlled LLY?
A. Try it and find out. I have tried it on a few different OS's and an 07 classic. I haven't ever flashed the newest, so I cant say about that one.

Q. Will this work on my '04.5 to early '05 LLY?
A. Yes, but it (the ECM) doesn't use the turbine for braking. Instead, just like the MD's for that year range use a flapper in the exhaust to act as the brake. I have tested it and it does power a pin to activate a solenoid for the flapper valve on the LD trucks. Figure it out for your self. Apply the knowledge learned here to your LLY and you'll figure it out.

Q. Does this work for LMM's?
A. I have done very little messing around with it on an LMM years ago and I cant tell you which OS I did it on, but the logic in the ECM is there but doesn’t activate the brake. It does send the TCM into the same down shifting pattern as the LBZ but nothing happens with the turbo. Again mess with it your self maybe you can figure it out.

Happy braking!

 

[bison]

I took another load down to the butcher last thursday.
I pushed the tow/haul button,light came on and stayed on,..been working ever since.
Sure affectted the mileage though, i used a 1/4 tank more than with the first load,..pretty near same weight at 19000 + lbs

 

[THEFERMANATOR]

I took another load down to the butcher last thursday.
I pushed the tow/haul button,light came on and stayed on,..been working ever since.
Sure affectted the mileage though, i used a 1/4 tank more than with the first load,..pretty near same weight at 19000 + lbs

That's odd. I know mine uses alot more fuel out of tow haul mode when towing our travel trailer. In tow haul I can get 11-12, ot of tow haul mode trans temps sky rocket, and the milage drops down. Not to mention how much more I have to use the brakes when towing out of tow/haul than with it.

 

[bison]

1/2 a tank first trip.no T/H
3/4 tank sec trip with T/H only one way when loaded
450 km round trips.
Tank was full till the cap, i gravity fill from my bulk tank so no foam.

 

[RI Chevy Silveradoman]

My truck uses more fuel with the tow haul as well. It is normal due to the higher shift ranges and higher RPM's. But the transmission temps with the Allison are cooler and it keeps the engine in the proper sweet spot for better performance.