Dead Alternator

[andy685]

2022 cummins 3500 with Dual Alternators. It appears one is not functioning. Started by getting low voltage warning on my dash. Showing 10 volts. Truck ran fine and I was thinking it was the voltage sensor. Today on the way home it dropped to 9 volts and the truck went a little crazy. Dash went dark. Radio turned off. No Power steering. Got it home. Passenger battery is 13 volts with the truck running. Driver battery is 6.8 volts.

I assumed these two batteries were connected to each other but it appears not to be the case. I don't need dual alternators. Has anyone ever not replaced a bad alternator and simply ran a battery cable between the two batteries?

 

[Trash Panda]

One bad battery will quickly destroy the other remaining good unit

I’d wager a new set of batteries fixes the problems, and the alternators are fine. Have you tested them?

 

[AH64ID]

2022 cummins 3500 with Dual Alternators. It appears one is not functioning. Started by getting low voltage warning on my dash. Showing 10 volts. Truck ran fine and I was thinking it was the voltage sensor. Today on the way home it dropped to 9 volts and the truck went a little crazy. Dash went dark. Radio turned off. No Power steering. Got it home. Passenger battery is 13 volts with the truck running. Driver battery is 6.8 volts.

I assumed these two batteries were connected to each other but it appears not to be the case. I don't need dual alternators. Has anyone ever not replaced a bad alternator and simply ran a battery cable between the two batteries?

The batteries are tied together in parallel, the cable runs across the aft of the engine bay under the cowling.

Are you getting any codes?

I’m also willing to bet that the one low voltage battery is shot and both alternators are fine, but if you run around with bad batteries like that for too long the alternators will quickly wear the brushes out and fail.

What’s odd is the power steering not working, are you referring to the assist portion or at all? If it’s any power steering then you could have a failed serpentine belt but the other symptoms simply point to a bad battery.

Lastly, you can revert to a single alternator by removing the one by the intake horn, putting the standard belt on, capping the control wire plug and reprogramming the truck for a single alternator (AlfaOBD or JScan can do this).

 

[andy685]

The batteries are tied together in parallel, the cable runs across the aft of the engine bay under the cowling.

Are you getting any codes?

I’m also willing to bet that the one low voltage battery is shot and both alternators are fine, but if you run around with bad batteries like that for too long the alternators will quickly wear the brushes out and fail.

What’s odd is the power steering not working, are you referring to the assist portion or at all? If it’s any power steering then you could have a failed serpentine belt but the other symptoms simply point to a bad battery.

Lastly, you can revert to a single alternator by removing the one by the intake horn, putting the standard belt on, capping the control wire plug and reprogramming the truck for a single alternator (AlfaOBD or JScan can do this).

No codes. Just the dash lighting up like a Christmas tree then going completely dark.

I had thought the batteries were dead a day ago when the truck wouldn’t start. They were replaced with new batteries on Tuesday. Wednesday evening is when the driver drained to 6 volts while while passenger stayed at 13.

I did check the voltage coming from the driver alternator. It registered zero volts after I disconnected it from the battery.

As for the power steering it was the assist portion. I could steer but it was like the old cars.

 

[AH64ID]

The battery should be similar since they are in parallel. Check the battery connections, but it’s very possible you got a bad battery with your new ones. Did you replace them or have them replaced?

A bad alternator should give a code.

The lack of any power steering is odd thou, that’s not electric and driven by the same belt that drives the alternators. The one battery at 13V suggests the belt is spinning.

 

[andy685]

I replaced the batteries myself. I checked all the connections last night. But will check again. My confusion is why the driver alternator would register 0 volts unless the computer manages which one produces power.

I’m gonna pull the battery to have it tested.

 

[AH64ID]

Yes, the ECM manages them. I’ve read that the 2nd (drivers side) will not work until the main (pass) is substantially loaded. That’s not how I would have programmed it, but allegedly Ram did.

When the power steering doesn’t work how do your brakes feel? They use the same hydraulics.

Did you check the alternator supply fuse?

 

[andy685]

Brakes were fine. At least I think they were. I was going slow by the time all that went out.
With the alternator fuse are you speaking of the block fuse between the battery and the alternator cable? If so, yes I did check that, it ohms out ok. If you are talking about a fuse in the fuse box, I don't know which one it is.

I guess I'm still getting hung up on the batteries being at different voltages if they are connected. I think I dig into that connection a little more. Does it have a fuse that could have blown which is preventing the pass thru charging from the passenger battery? But, maybe that is what you mean by a bad battery... maybe it isn't taking a charge.

And AH64ID, thank you for the responses.... talking this thru with someone does help.

 

[andy685]

Trying to think of a way to test the battery.... How does this sound?

Disconnect the driver battery (one with low voltage). Connect it to a battery charger to see if it will take and hold a charge.
If it won't, bad battery and I can replace it.

If it will...then....

With the driver battery disconnected connect the battery charger to just the driver side cables. If the pass thru cable is functional shouldn't that provide charge to the passenger side battery?
If so, and I don't get a charge then I can assume something is wrong with my pass thru cable.

 

[andy685]

Just realized I started this in the incorrect thread. Anyway to move it to Gen Discussion?

 

[Trash Panda]

Trying to think of a way to test the battery.... How does this sound?

Disconnect the driver battery (one with low voltage). Connect it to a battery charger to see if it will take and hold a charge.
If it won't, bad battery and I can replace it.

If it will...then....

With the driver battery disconnected connect the battery charger to just the driver side cables. If the pass thru cable is functional shouldn't that provide charge to the passenger side battery?
If so, and I don't get a charge then I can assume something is wrong with my pass thru cable.

Remove both batteries, and take them to a parts store to be load tested.

It is a free service.

 

[andy685]

Trash Panda... I don't disagree that would be the best solution.
But I think I would need to get the low voltage battery fully charged prior to having the load test... So I was just thinking my above "experiment" might point me in the right direction.

I'm going to try my test tonight after work... If I don't see any issues I'll pull the batteries and take them to the parts store tomorrow after work.
Sucks that work keeps getting in the way of doing stuff!!!

 

[Trash Panda]

Trash Panda... I don't disagree that would be the best solution.
But I think I would need to get the low voltage battery fully charged prior to having the load test... So I was just thinking my above "experiment" might point me in the right direction.

I'm going to try my test tonight after work... If I don't see any issues I'll pull the batteries and take them to the parts store tomorrow after work.
Sucks that work keeps getting in the way of doing stuff!!!

Even if it takes and holds a charge, you still need to load test it.

 

[superjoe83]

Double check all of the connections including grounds, I took a couple pictures of my '22 battery connections for you to use as a reference to confirm everything is correctly connected. Ignore the red ring terminal on the drivers battery, that is my battery maintainer.

I would suspect a bad connection on the crossover cable.
If you have a volt meter with the truck running put one lead on the positive of the right battery, then put the other lead on the positive of the left battery, the reading should be close to zero, if you show voltage then you have an issue with the crossover cable or a connection somewhere.
You should also do the same test with the grounds of the batteries.

This assumes the right alternator is functional since the right battery seems like its charging according to your earlier post?

 

[andy685]

Double check all of the connections including grounds, I took a couple pictures of my '22 battery connections for you to use as a reference to confirm everything is correctly connected. Ignore the red ring terminal on the drivers battery, that is my battery maintainer.

I would suspect a bad connection on the crossover cable.
If you have a volt meter with the truck running put one lead on the positive of the right battery, then put the other lead on the positive of the left battery, the reading should be close to zero, if you show voltage then you have an issue with the crossover cable or a connection somewhere.
You should also do the same test with the grounds of the batteries.

This assumes the right alternator is functional since the right battery seems like its charging according to your earlier post?

View attachment 91830
View attachment 91831

SuperJoe,
Thanks... the pictures match my setup exact. At least I know I didn't miss something with the swap.
And thanks for the suggestion for checking the crossover cable... I do that this evening.

 

[andy685]

SuperJoe...voltage between Positive terminals was 1.5 volts....negative was 0. I'm assuming that is showing the crossover cable as ok.

I did reconnect everything except the driver alternator and used a jump pack to start the truck and keep it running. Today the drive alternator was outputting power.

I did pull the batteries and take them back to the auto parts store. Told they they were not charging under load and I would like to replace. They did no questions. I did have them test the new batteries before bringing them home.

Connected... started right up. Both batteries are getting a charge. Showing 14 volts on the meter and in the cab. Drove 5 miles with no issues.

I'll update again tomorrow.

TrashPanda.... thank you for the assistance and recommendation to replace the battery.

AH64ID... thank you for all the information and troubleshooting steps.

I'm really hoping this problem is behind me. Found out last night the furnace in my RV went out and now its frozen... fix that next and then check for leaks before my trip to Florida.

 

[AH64ID]

Glad to hear you’re getting normal voltage.