LMM driver side battery not giving power

[Duramaxduner]

Hi everyone, I have a 2008 LMM. The truck has always turned over very slowly and takes a second to start. I thought it was just a dead battery but I'm afraid its something more. If I disconnect the passenger side battery so only the drivers side is connected, the truck is dead, only the check engine light shows up very dim. If I unhook the drivers side battery so its only running off the passenger side, everything comes on like normal. Its obvious to me its just cranking off the passenger side. The drivers side battery tested at 12 volts. I also put a new battery in the drivers side and still the same slow crank. My next guess is maybe the drivers side battery cables are bad? Maybe it could be a ground? I don't know why the drivers side isn't giving any power when the battery is good.

 

[JoshH]

I had an 08 LMM in the shop a few weeks ago that wasn't making good contact on the negative battery post of one of the batteries. I can't remember which battery it was, but if you disconnected the battery that was making good contact, the truck wouldn't do anything.

 

[Dozerboy]

I never looked to see how our batteries are wired exactly. So by unhooking the drivers side battery you might be unhooking both batteries. You do have some kind of issue in regards to the slow cranking. Have you had the batteries load tested?

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[Duramaxduner]

The thing is, when I unhook the drivers side battery is when nothing changes. The truck starts up and runs fine-acts normal. Its when I disconnect the passenger side. I know a Duramax can run on one battery because when I was up north one time, my buddys battery exploded in his blazer and I gave him my passenger battery for the weekend, I drove around all weekend with one battery. I have checked both connections at both batteries and they are both making good contact.

 

[bmc1025]

follow the ground wire and check the connection

 

[JoshH]

You have a bad connection somewhere or a bad battery.

 

[Awenta]

Or a bad wire. Test them all one by one. Start by testing the batteries though.

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