i also wanted to note that when I hooked my battery charger up it was reading reversed when hooked up correctly.

 

Addressing the polarity issue here: Have you ever charged those batteries (or attempt to jump them?) and did you use an AGM specific charger? If your multi-meter is reading this way, there is a chance your charger was hooked up wrong when charging a depleted battery or you depleted on a jump with cables reversed. Chances of reversing polarity on a battery is rare however.

Ron gives good advice here. Interested in what you find out.

 

I would unhook batteries and load test them.

 

X2 on the load test - or use a hydrometer. Sounds like the battery is so sulfated that the plates are touching - my bet is new batteries will solve all your issues.

 

They are Odyssey AGMs. They are only 1.5 years old. I will load test but not sure. I am getting 12.6 Volta from each battery with a meter.

 

Disconnect one battery negative cable, check voltage at that battery, then check the other battery. Then reconnect first battery negative cable. If both batteries are hooked up, you are checking the combined system, not either individual battery. Try starting with just one battery hooked up, then the other. Truck should start with just one battery if it isn't to cold.

Check the output at your megafuses, maybe on the firewall near the passenger side battery - not sure for your year of truck. Check battery grounds on the side of the block near the front, just above the oil pan. If you live in salt country, make sure the ground from the firewall just inboard of the master cylinder to the back of the block is in good condition.

 

Disconnect one battery negative cable, check voltage at that battery, then check the other battery. Then reconnect first battery negative cable. If both batteries are hooked up, you are checking the combined system, not either individual battery. Try starting with just one battery hooked up, then the other. Truck should start with just one battery if it isn't to cold.

Check the output at your megafuses, maybe on the firewall near the passenger side battery - not sure for your year of truck. Check battery grounds on the side of the block near the front, just above the oil pan. If you live in salt country, make sure the ground from the firewall just inboard of the master cylinder to the back of the block is in good condition.

I will do that when I get home. Thank you! I have no grounding issues unless something ate into the wires. I drive the truck regularly and live in Northern Nevada so no salt or climate issues. I am so praying this is just a battery issue. The truck has been perfect till this. I have just never had any issues with Odyssey Batteries before.

 

So I load tested the batteries and charged them for good measure. The batteries read good and are now fully charged and no change 😕. Going to start testing fuses in all three locations and if I can’t find anything there then it’s time to call in the professionals 😭

 

see here: 2015 duramax dually no crank, no ecm power

Could it happen 2 times, same place?

 

So I tested fuses in the drivers side panel and the ONLY fuse that gets power is

see here: 2015 duramax dually no crank, no ecm power

Could it happen 2 times, same place?

thank you Ron. I’ll look through that thread.

 

So I tested fuses in the drivers side panel and the ONLY fuse that gets power is fuse 14 the switch back lights. So I’ve seemed to narrow it down to no power to that fuse panel. I check the fuses with an ohm meter and all fuses are good. Now I am researching how that panel gets its power.

 

So I found the problem!!! It is a fuse at the battery. Now I just need to replace that part. I tested all those fuses and I had power to all except the red circled one. Made a little jumper and BAM works as it should. If you look close you can see the deformity by the fastener. I also found this https://static.nhtsa.gov/odi/tsbs/2014/SB-10058154-8454.pdf

 

Do you know the part number to replace this? Thank you for the find and forum post. This helped me find the issue quickly.

 

Good job. This will help out others in the future

 

Nice work and kudos to you for doing the test with your handmade jumper to test and prove your proposed fix.

 

I think I found the part. You have to order, not something you can get at any auto parts store. You can temporarily fix this with a little soldering. Use a Dremel to cut the little plastic nubs off of the cover over the fuses (between the bolt and large metal piece) then you can dab a little solder on to fix it. Be aware that you will probably not get the same amp rating but it will get you by until the new part arrives. I think mine broke because there isn't anything really keeping those little solder joint fuses from wiggling around. I just had a ton of work done due to my CP4 failing and I think all of the moving around of wires and stuff allowed that fuse joint to wiggle back and forth enough that it weakened/cracked. Then it finally couldn't handle the normal amp draw on start and popped. Be careful bridging to the next stud because on mine it was a lot smaller of a fuse and you run the risk of popping another. I'm also curious why yours says 250A and mine says 175A but we are both 2015 LML? Mine Is a Denali HD.