2 Battery Question

[excal66]

New to the internets looking for some guidance.I searched for my specific issue but couldnt find anything about it so here my info..

 

2001 Silverado 2500hd 8.1l vortec with the allison.It has 2 batteries under the hood.One is reading 12.5 volts off and 13ish running and the other battery reading 3.4 volts running or not.

 

Are both batteries suppose to be 12+ ?I have never had a truck with two before.

 

I have been getting the p1781 code which is improper voltage for the tcm to ecm and my truck has been sputtering at low rpms but when I get on it it runs fine.Fuel filter,air filter,etc are all new.

[txab]

You've got a bad battery replace it. If they are the same age, replace both of them at the same time

[sdeeter19555]

Yup, what he said...it's best to replace batteries in pairs when you can.

 

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