Voltage drop

I have a 2019 Ram Rebel 5.7L Hemi. Just recently I have noticed that the Battery voltage while running starts around 14.6v and is dropping to 13.4v, Around this point things start getting haywire, Service Shifter, Service Airbag, Traction control service, Trailer Brake lights all start going off.
I have been to 3 different mechanics. 2 say nothing is wrong and they reset the codes and say come back when it triggers. a 3rd says they are seeing Low charge current from the Alternator.

Any suggestions

Do a proper load test on the battery. If it is good then the most likely culprit is the Alternator not putting out enough or the regulated voltage is not correct. Both of those are easy enough to test for.

what should be the proper voltage output from the Alternator. I have seen so many different numbers and ranges. Curious

Double click to expand. In terms of voltage output, between 14 and 15.2 Volts for most post 2016 Ram is normal, depending on the amount of draw on the system. You need to test the alternator to esnure it can output in that range as needed, as well as produce the AMPs required. (The RPM is alternator speed, not engine RPM. That is what the pulley accomplishes, higher RPM on alternator versus engine speed.)

With the engine running and measuring voltage at the battery terminals, the alternator should be putting out min 14V, usually 14.2 to 14.8, depending on how long after start up. Higher just after start, maybe even in 15 range, normally not below 14.5 till it has been running a long while. 13.4 volts is not enough to run the vehicle properly, that is why you are getting all the error codes. These trucks are heavily dependant on proper voltage for everything to work right.

Check battery ans alternator for loose connections. Also clean the battery posts if you haven't done it in the last few years.

did you ever figure this issue out? I'm having the same issue with noticing that the voltage sometimes drops down into the 13s, and I get the service shifter service airbag system. sometimes I get stranded for a little bit, I had my battery tested and it is fine, I'm thinking about replacing my alternator with a high output alternator and seeing if that solves it since I've got about 200,000 mi on the original alternator

appzattak said:

did you ever figure this issue out? I'm having the same issue with noticing that the voltage sometimes drops down into the 13s, and I get the service shifter service airbag system. sometimes I get stranded for a little bit, I had my battery tested and it is fine, I'm thinking about replacing my alternator with a high output alternator and seeing if that solves it since I've got about 200,000 mi on the original alternator

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Good luck getting an answer. Showed up June 3, 2023, got the info, last seen June 3rd. Not even the courtesy of a thank you or a post about how it gets fixed. About 95% of new memebers that come on and ask for help follow this pattern. I rarely answer first time posts anymore because of that.

So my suggestion, follow the information in this thread and I bet you figure it out. If you need more help once you have followed the steps post back and we will see if we can help.

I also need a high output alternator as my new stereo draws too much, I’m fine during the day but when I use Lights or AC my voltage drops. I have seen some alternators up to 400amps

If you have massive draws on your system, a higher output alternator isn't the only thing you may need. You may want to look at installing a second battery and splitting the load between the two batteries. Typically you run the sound system off the second auxillary battery. That leaves the main battery to run the trucks systems with normal draws.

To be clear, the batteries should be exact make, rating and age, and you need to up the alternator output, or run dual alternators. Just adding a second battery isnt enough without upping the amperage being supplied to them.

The tester at OReilley Auto or Autozone can load test the battery and do an alternator test. I'd start there...for guys who are seeing electrical flake-out.

Bear in mind a glazed belt, worn alternator pulley (which doesn't fit into the belt very well), or even a weak belt tensioner (although less common), can also cause slippage of the alt pulley under load. Which means it would show lower charging. So...that means a guy could drive around all day w/o problems when there isn't much load on the pulley (not slipping), but a long drive at night with lights and the AC on (more load = belt slippage), could drain the battery down. But after driving it around the next day it charges up (enough). When this scenario occurs, it's hard to pinpoint a bad belt/alt, etc right away till the point the vehicle runs wonky or doesn't start. But the root could be a slipping alt pulley.

So if a guy gets a 'low alternator' warning, check those things before condemning the alternator right away. And remember, if an alternator pulley has been slipping, it's gooves might be worn and will not fit into a new belt very well. Just something to be aware of.

Excellent points JW. Serpentine belt is an often overlooked maintenance item that can affect performance. Pulley can too but a lot more rare. Still worth looking at.

I'm a about to pull the trigger on this alternator, just need to find a slightly shorter belt.

Dean2 said:

Good luck getting an answer. Showed up June 3, 2023, got the info, last seen June 3rd. Not even the courtesy of a thank you or a post about how it gets fixed. About 95% of new memebers that come on and ask for help follow this pattern. I rarely answer first time posts anymore because of that.

So my suggestion, follow the information in this thread and I bet you figure it out. If you need more help once you have followed the steps post back and we will see if we can help.

Click to expand...

Thanks for the info Dean. I already made sure the battery cables are clean and secure. I had Les Schwab test the AGM batter that is only 2 years old and it is cranking over specs and is good. I checked the alternator connections and the "look" ok. I sprayed with some electrical cleaner for good measure on the connections. I really hope to figure this out once and for all.

I will definitely keep folks updated here and on other thread I have going, because this is so annoying, specially when you get stranded because of the shifter not working.

Have them test the amperage and voltage output at different engine rpm. Alternators don't usually go bad slowly, they normally work or don't but it is possible that something is weak or failed and causing low output.

Dean2 said:

Have them test the amperage and voltage output at different engine rpm. Alternators don't usually go bad slowly, they normally work or don't but it is possible that something is weak or failed and causing low output.

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I have been wanting to get a new alternator for a while. I do run many aftermarket goodies on my truck that did not come with it. I have a nice system with two amps, an Audio Control LC7i, 2 12 subs, 4 sets of components. I've added a 8.4 uconnect, backup cam, heated seats, heated wheel, fully tuned with monitor, wired in escort radar...probably more that I have forgotten about, but I think I could use the additional ampage and hopefully fix the seemingly electric issues that I have been having.

This all started with getting the service shifter, so I bought a brand new one and replaced it, still had the problem and at the same time I started getting the Service Air Bag system, that happens constantly when driving. The service shifter happens way less frequently, but still happens and occasionally will strand me, but if I wait a while it will start to work again.

BTW, I bought the new alternator, I will hopefully get it in this weekend and report back.

I got the new Mechman 370 amp Alternator installed, still had the Service Air Bag, and just yesterday had the service shifter outage, waited about 10 mins with truck running and it came back on. So there is still something else wrong...where to look next?? I really don't want to take it to the dealer I a think they will jsut spin their wheels guessing and still charging me.

Take it to a specialist Auto Electric Shop. They will track it down for you. My bet is that one or more of the many added on features is causing the issue.

Dean2 said:

Take it to a specialist Auto Electric Shop. They will track it down for you. My bet is that one or more of the many added on features is causing the issue.

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I will try to find a specialty shop, but will be hard, I refuse to take it to the dealer as they will just suggest new parts that I have already replaced. I don't think any of my added features could be the problem as there are numerous folks on this forum with the exact same problem, and I'm betting they are not as modded as mine.