I thought Id start a thread for LMM users to let you know about the experience I had hooking up a Turbo Brake in my 08 LMM. I got the idea from a previous thread that was directed at LBZ and LLY engines. There was a side note indicating it worked on LMM so I thought Id give it a try.
I am certainly not trying to take credit for this idea, just repackaging it. The link to the original thread is: https://www.duramaxforum.com/forum/h...-new-post.html
in that thread near the beginning is a link to another thread in a GM forum. It gave information about getting to the C2 connector on the ECM. I suggest you go to that thread as well to glean what you can from that thread.
My total cost was less than $12.00 for a round toggle switch and mini-incandescent indicator light. I was fortunate enough to obtain the two pins I needed from the local GMC dealers service department.
An Avionics Tech at work put two 8' leads on the pins for me. He had the special crimping tool necessary to connect the Molex pins to the wire. I found the pins online at a cost of $8.00 each plus shipping making the total cost around $35.00. Total cost still under $50.00
As for how it works....When the pin in location 53 is grounded the Turbo Brake is activated and on. It does not matter if you are in Tow/Haul or not, it is ON. I found this out by first grounding it directly without the switch and taking it for a ride. I did not want it on all the time so I went back in and installed the switch.
I was adding a Power Steering Fluid Cooler the same day so I had already pulled the LF tire and Lt Fender Skirt this gave very easy access to the C2 Connector of the ECM which is right there on the left side. I did all my work on that connector seated on a work stool rather than leaning over the fender. I thought it was MUCH easier.
I did install the indicator light first thing and it works perfectly too. I made this one green because directly above it is a red indicator light. This is for my fuel transfer system to let me know it is transferring fuel and I did not want to misconstrue what the lights were indicating.
I only finished this yesterday so I have not yet had an opportunity to tow my Fifth Wheel with it. I am REALLY looking forward to using it for this.
I did go out today and see just precisely what it does and here is the test drive info. I began at 65 MPH, 1650 RPM (6th gear), no T/H and TB switch on. When I let off the gas the indicator light illuminated a couple seconds later, a couple seconds later a slowing of the vehicle occurred and the transmission downshifted to 5th-RPM went up to 2100. As soon as the RPMs dropped to 1500 another downshift occurred taking the RPM back up to 2100. This cycle continued with the turbo slowing the vehicle significantly and the transmission acting as if it were in TH mode. It brought my truck down to 15 MPH before I accelerated slightly and turned the Turbo Boost Switch off.
All in All I LOVE the mod. It was cheap and will be VERY useful.
A HUGE Thank You to all who wrote the original threads and who provided me ideas and encouragement.
A couple pics to show the installation: