Alternator stopped charging last night, ok this morning?

[Blakers]

Last night my alternator stopped charging when I left work. Truck was running on 11.8 volts all the way home with headlights on (15 miles). Got home and I checked under the hood. Belt ok. Alternator turning. I tapped on alternator with a hammer in case a brush was hung up. No change. This morning I started truck and it's charging fine, putting out 14.5 volts.

My truck is an 03 and I replaced the original alternator with one from Advance Auto Parts in 2016 when it failed in Virginia on my way to the Outer Banks in 95° temps. That alternator failed 9 months and less than 18,000 miles later in 2017. This one has been ok until now, and probably has 100,000 miles on it.

Why would an alternator stop charging last night and then be ok today?

Thanks.

 

[DavidC]

The only way I see that happening is a loose connection somewhere like the field wire connection on or in the alternator, maybe the PCM or whatever controls the field on your year, mine is the PCM. If the controller had a brain fa*t that could happen also.

 

[Tuesdak]

Worn out brush or stuck to where the " Static Vibration Test" didn't help. Cracked connection in alt somewhere. Never hurts to inspect all connectors to it including a loose battery connection. Load test batteries is a good idea.

I am guessing it's under a lifetime warranty so swap it out...

FWIW get a "NEW" alternator not a reman that is simply a "repaired" unit. Parts stores are in a race to be CHEAP... Otherwise find a local rebuilder and have it rebuilt. You can check the brush length yourself to pinpoint failure. Kits are available to repair it.

 

[Ozymandias]

Did it really not charge, checked with a fluke or was it your dash voltmeter showing 12 Volts?

 

[Blakers]

Thanks. It charged fine today. No problems at all. So ??? Maybe just a fluke?

I generally don't buy from Advance or Autozone if I can help it, but I was on a vacation trip and needed it immediately. I still have my original and plan on ordering a rebuild kit from Geno's.

Worn out brush or stuck to where the " Static Vibration Test" didn't help. Cracked connection in alt somewhere. Never hurts to inspect all connectors to it including a loose battery connection. Load test batteries is a good idea.

I am guessing it's under a lifetime warranty so swap it out...

FWIW get a "NEW" alternator not a reman that is simply a "repaired" unit. Parts stores are in a race to be CHEAP... Otherwise find a local rebuilder and have it rebuilt. You can check the brush length yourself to pinpoint failure. Kits are available to repair it.

 

[Blakers]

Correct, it did not charge. "Check Gauges" light came on and instrument "volt meter" went to zero. A real voltmeter read 11.9 volts, and then, when I got home, read 11.8 volts. But, after I shut the lights and the engine off, it read 12 volts. Started fine in the morning. Spun right over as if the batteries were strong.

Did it really not charge, checked with a fluke or was it your dash voltmeter showing 12 Volts?

 

[Tuesdak]

I LOVE it when things give me a warning rather than failing completely. (Again inspection of connectors is highly recommended.) I suggest ordering the rebuild kit ASAP and then carry it as a spare: AFTER TESTING! Nothing like lugging a NIB spare alt around for 50K, bolting it on out of need and the SOB turns out to be DOA. I don't even leave a parts store before making them test a alt or starter anymore: because NO ONE ELSE DID after repair/rebuild/new.

 

[Dick Langendorff]

I had something similar a while back. Replaced the alternator. Everything was fine for a while. Then it seemed the batteries were a little low. I grabbed the post wire that goes from drivers side to passenger, I stood there holding the wire. That #2 wire was completely corroded away.
New wire from battery to battery, bingo. No issue.
Before you buy another alternator, check all of your connections.
Worth a shot.

 

[Blakers]

Does anyone know how much voltage it takes to keep the common rail Cummins running?

 

[Ozymandias]

I have seen mine running on 11.5 once.
But was started on a higher level.

Don't know when it will cut out.

 

[Blakers]

I've seen mine running at 10.something with the grid heaters on.

My 12 valve would run with no power whatsoever as long as the shutoff was wired open. Diesels sure were reliable back before computers!!

I have seen mine running on 11.5 once.
But was started on a higher level.

Don't know when it will cut out.

 

[Ozymandias]

The ECM runs on 5V, so does all electronics in vehicles.
The point is when will the other systems quit working? I dont know.

 

[CVR222NV]

My recollection is that it was around 6.5V. I make a 200 mile trip to our ranch in east central Nevada from Las Vegas and about 1/4 way noticed the voltage dropping. I checked to see if I had thrown the belt but everything seemed to be working fine. At the half way mark the voltage was below 12V. I texted ahead to let everyone know I was having charging issues. Truck eventually went in to what people describe as limp mode at around 8V and finally died at around 6.5V in an area where there is no cell service. When help arrived around 4 hours later the sun was high and when I was inspecting the alternator again I could see that the connector plug had come apart. Plugged it back in and jumped it and has worked fine since. I now have a dedicated flashlight in my truck! BTW, while I waited with the hood up and doors open on the side of the highway not a single person stopped to help. When I see people stranded I always stop to see if I can help even if it's just to make a call when I get cell service.