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Hey I’m new to the site. I have had several duramax trucks from 05 2500 to 12 2500. We use these trucks as a pice of equipment. So I hate to say they all get ran hard. We use them to move our tractors around they always are pulling a trailer. I always try to do all repairs my self. My 09 3500 4x4 220000 miles just started for no reason without a trailer hooked up will put out full trailer gain. You will be driving down the road and look down at the message center and you will see full gain. Just driving down the road not pressing the brake or anything. So I tried sliding the manual switch back and forth but nothing. It will also do the same thing with a trailer. Cost me a set of trailer tires. I’ve set the gain to 0 so it will not lock up the brakes but it will still every now and then put full power on the dash. Never had the check engine light come on or service trailer brake. I can’t find anyone that has had this issue? Any ideas?
 

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Thanks for the input. What’s your thoughts if I ran a new wire to from the fuse box to the power supply on the controller?
 

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Why not just test the existing wiring? And fix it if there's a problem.
 

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I’m also brand new to this site and I have the exact same situation I think. The Brake pin on the 7 way always reads 1.3 volts which in return always has the trailer brakes engaged slightly causing it heat up bearings and tires! I have changed the plug and the control relay module and still the same. Also soldered the wires after I put new plug on. Any info would be greatly appreciated!!! Thanks I’m advance
 

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The LML and newer trucks have a different system (slightly) than LMM. The information below is for my LMM.
If you have a code reader that will read 'C' codes see if there is anything recorded for your truck. O'Reilly auto parts have nice Bosch scanners that will definitely read the C code. While the newer systems work about the same, the relay and TCBM module are physically different and pin numbers between the two systems just don't match up.
It may be worth getting a subscription to ALLDADIY.COM to see what troubleshooting/verification/diagnostic applies to your truck.

Below is a link with more detail, pertaining specifically to LMM or older models, but may be helpful to your case.
Chevrolet Silverado 2500 HD Wondering if one of the GM techs…
 

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I just checked my truck and there is no voltage between terms 1 and 2, 7PM and 5PM positions respectfully on the bumper 7-way connector. If you have voltage, I would see where that voltage is coming from.
 

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Thanks I will definitely look into that. Also I get the 1.3 volts when I go from ground to the 5 o’clock pin with the key on. Thanks for your help
 
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