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Discussion Starter #1
So I have been having this issue for about a year now, thought it was batteries so I bought 2 new AC Delco batteries rated for my truck last year. All was good for a while and then started acting up again, took the truck to a GM dealer and after diagnostic they said it was the starter, so they replaced it about a month ago. Out shopping a couple of days ago the same thing happened, click but no start, got a boost and it started, went to the garage and had the batteries tested and all is good. I have checked the cables including the junction box on the fire wall and all seem fine (no corrosion). I have tested the alternator with my volt meter(14.6 volts when running). Any ideas would be greatly appreciated.
Thank you in advance.Ed
 

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Have you checked the grounds? While I am new to the LMM world why past experiences always seem to point to a bad ground in these cases. Seems you should have a ground from each battery to the block.
 

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I seem to recall a rash of poorly crimped battery cables on the '07.5s and '08s. Thorough inspection of where the cables are crimped into the battery lugs is in order.
 

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Discussion Starter #6
I still haven't found "smoking gun" but my suspicion is because my commute to work is 10 minutes, living in a cold climate, and not using my truck on the weekend the batteries don't get fully charged. I changed the alternator to a higher output one(160 amp) and so far so good.
Thank you to every ones input on this issue.
 

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Short drives like that are tough on both the charging system and the engine especially in cold weather. If you can, I would try taking a long alternate route to work in order to allow the engine time to come up to operating temp and the charging system to recover the batteries. The generally accepted recommendation is to drive for 30 min which will allow all fluids to come up to temp and battery to top off.
 

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Final Solution

Good Morning-

I spent 6 months with my LMM chasing this same/ similar issue. This why I got a great deal because the electrical was more than the dealer wanted to fight with and there was a little body damage.

I summarize what I learned as follows:

Using the entering argument you have tried all the basic checks and have eliminated the security and airbag system and you have the correct rev to the operating system in your PCM Here is what I found: based on reading a ton of bulletins and every website I could

1 the battery junction box on Passenger side firewall. It is a likely problem. Pop the plastic cover off and clean the connections (unhook batteries first)

2 when you have done that the "positive side" of the battery electrical should be sound

3 if no smoking gun was found (ie heavy oxidation) look at the negative side cabling. Start the truck and verify you have >14 volts on both batteries (14.8 ish) If not you have a cable issue. Almost all the trucks came with RPO code TP2 which is direct parallel battery hook up. There is also 8B0 for the add on digital battery isolator.

I found that I had 12.4 volts on the "aux" battery (pass side) and that the negative cable was corroded on the inside of the molded lead connector. Therefore it would periodically charge and work but only once in a while.

That caused the truck to try and pull all the starting current from the Drivers side battery (it killed it in 7 months)

I took and unhooked all the batteries and did connectivity (resistance checks) on all the cables. I replace the pass side battery ground and now it all works as it should.

I cant take much credit as I found post on another forum that got me started. That guy had a bad terminal end on his positive on aux battery (still caused same problem.

I hope this helps I spent a very long time chasing this. I know how frustrating it can be especially when you pay people to tell you there is nothing wrong or we couldn't get it to repeat.

if you have specific questions PM and I will help you out. I also know how frustrating it is when you get no help
:thumb::thumb:

good luck
 

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Discussion Starter #9
Since I have changed the alternator it hasn't happened, but I will check the inside of the cabling though.
Thanks for the info, greatly appreciated.
 
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