2011 6.7 Liter Cummins - 3500 Mega Cab Charging Issue Troubleshooting Help

Scenario:

Truck has 132,000 miles with no history of electrical charging issues other than having to replace the stock batteries that had an exceptional life of 10+ years.

Scenario: I stopped at a location and left the truck running, upon my return and getting ready to drive away from the location the Radio immediately powered down. No concern as the stock radio has been somewhat of a PITA during ownership i.e. loosing radio channels and inconsistent Bluetooth connectivity that would result in the radio locking up; only resolution was to pull the fuse to the radio to perform a hard reset which to me was a non-issue. So I thought this was the problem, turned off the truck and upon a restart the truck was completely dead. Couldn't even turn it over, place it into gear and the key fob was locked in and there was no "Battery" low voltage fault prior to this event.

I was fairly certain at the time that the alternator had failed simply based on the fact that the batteries are new with less than 2 years on them. Alternator was replaced however the low "Battery" voltage error continued (Which is a new Fault) and is still continuing. I've performed the following troubleshooting:

• Verified that I have no crossover cable voltage issues by validating voltage is the same on both batteries along with cleaning all cables and ensuring tight clean connections.
  
• Verified solid connections at the newly replace alternator.
  
• Troubleshot a potential grid relay heater being open and replaced the relay just to be 100% certain that this was ruled out.
  
• Inspected electrical grounds with no findings.
  
• All fuses have been tested with only finding one fuse blown on a USB charging circuit. This was replaced.
  
• Tried to locate any fusible links that may have been damaged, primarily on the passenger battery and have no findings that would indicate any issues otherwise. The fusible links appear to be integral to the cables on this year of truck and there is continuity between both the positive and negative that come off of the grid heater relay which would indicate no break.

What additional troubleshooting steps should I take? Is there a battery fuse from the grid heater relay that I have not verified and where would the location of that be? Is this a potential PCM failure?

Any additional recommendations or troubleshooting help would be appreciated. My next step is to have the batteries load tested along with the new alternator before I even consider a PCM replacement.

 

What do the battery's return when fully charged with a charger, then rest for 12 hours and then measure them independently with good volt meter?

Because it is not uncommon nowadays to have 2 year old battery's fail especially in these trucks that demand a lot from them.

By the way, how is the state of updates for the trucks systems in the past? Have they all been done?
Usually if an Alternator fails the truck will tell you with a fault Code and not just let it run until it's dead.
I questioning that the Alternator was bad at all.

 

I'm questioning that the Alternator was bad to begin with as well; all updates for the truck have been completed to my knowledge. I haven't tested the batteries after a 12 hour charge and rest, what should the voltage be with a good set of batteries? 13.5?

 

I only bring this up because you don't mention if there was a load placed on the batteries during your voltage drop test. If there was not, then the test is not valid. The voltage drop test for the crossover cable should be done as follows:

* The engine should be disabled from starting. With fully charged batteries, a helper should crank the engine for about 15 seconds while you measure the voltage drop from one battery positive battery terminal to the other battery positive terminal (not the cables - the actual terminals). The voltage drop should be .1 volts or less.

Did you check to make sure there is battery voltage at the alternator output terminal? If there is not, the alternator cannot charge. A test tight works well for this check.

- John

 

Fully charged batteries with now draw and 3-4 hours rest should read 12.7V.

 

Can you hear the starter relay close? If you can hear the starter relay close, measure the battery voltage while attempting to crank. Should be 10v or better. If the voltage doesn't drop much from the batteries resting state when you try to crank, less than .5v, you have a bad connection or bad starter relay or starter. Once the engine is running the battery voltage should be 13.5-14.5v.
Hope this helps.

 

Just as an unhelpful FYI, modern vehicles do not use the traditional wire-type links, they use this modern style:

 

Where would this link be located? Is this the one attached to the passenger side battery housing?

 

The wiring diagram does not show a fuse link for the generator. But that does not seem safe when the wiring is direct from the passenger battery to the generator.

 

I think that I would be adding one before this repair would be considered done! Seems like it may have been an oversight in the design. My little diesel tractor is fused off the alternator to rest of the wiring, just in case there's an issue, protects the wiring from being smoked!

 

And from potentially starting a fire - a short to ground inside the alternator and now a cherry red heavy alternator output wire that is being continuously fed by a fully charged battery. Two batteries with our trucks. I like fuses.

- John

 

That's why I'm thinking it has to be built into the battery harness but not shown on the diagram.

 

Don’t all the connections on the battery have the fuses built in?

 

I need to get some spare fuses to carry on the truck like I did my old truck. I need to make a list

 

If there would be a fuse, or a fusible link, and would be blown- the ECM would set a Code.
Simple as that.

 

And I'd still like to hear about the state of the battery's.
We got side tracked into a fuse discussion that doesn't apply here.

 

And what's up with that grid heater continuity? I'm sort of lost in translation in this thread.

 

It’s always the batteries.

 

Chances are high that you're right.

 

Test the batteries!