Alternator Not Charging

[RoyMunsen]

I recently got a 2012 Ram with a 5.9L Hemi. The truck worked fine until it didn’t. While driving, it died alongside the road. It was still running but wouldn’t shift gears or move. I jump started it a few times to get home. Ultimately, the alternator is not charging. If I check voltage from the negative on the battery to the alternator stud, I get ~12V, whether it is running or not. This is what I have done so far:

• Pulled and tested the alternator — tested fine
• Replaced the alternator (twice) — still not charging
• Tested voltage at the battery — reads 12.6V (battery manufactured January 2026)
• Battery has drained a few times, so I trickle charge it to bring it back to 12.6V
• Inspected the PDC fuses — J13 (60A IOD-MAIN), J14 (40A EBL), M19 (25A ASD), and M21 (20A ASD) all have continuity
• Swapped K10 (ASD relay) and K4 (RUN/START relay) with identical relays — no change
• There are no blown fuses in the box
• Tested the ignition sense wire at the alternator connector — reads ~12V with key ON
• Tested the field control wire at the alternator connector — reads 0V with key ON and engine running, PCM is not sending a signal to the alternator

It just seems like the alternator is not being told to charge. Has anybody experienced this before? I’m trying to not take it to the dealership if I can avoid it.

 

[tron67j]

https://www.justanswer.com/dodge/ftk3y-nobody-tell-me-hope-can-does-2012-ram-1500.html

 

[Jeepwalker]

BTW, did you load-test the battery or test with a multimeter?

Reason I asked is I went through some charging 'issues' last yr not unlike yours. Bought a new premium battery in the fall of 2024 for a vehicle I have. When I got the batt home it took FOREVER to fully charge up. That should have been my cue to retuen it to the store right then and there! For the first few months the vehicle worked normally. Then started having issues. Figured ....you know, new battery, had been working fine ... the problems were elsewhere. After a lot of wasted time goofing around troubleshooting this and that, I finally did a batt load test. The battery failed terribly. My suspicion is the battery sat low on the store shelf sulfating...for who knows how long? Or was just defectively made. Regardless, they replaced with a new battery and not a problem since.

So it's worth doing a Battery load test if you haven't done so.

But in your case it sounds a lot like a fusable link. Let us know what the solutions is.

 

[Pushrod8Speed]

I'd check it as close to the PCM as possible to eliminate any harness issues. If nothing there and want to avoid dealer...

2010 2011 Ram 1500 5.7L Hemi PCM Alternator Output Testing & Mail-In Repair

This video highlights our PCM repair service for the 2011 Ram 1500 with the 5.7 L Hemi. We demonstrate how we confirm a no-output alternator field driver fau...

youtu.be

 

[RamDiver]

A battery load test with a toaster-style battery load tester is always a great idea with our rolling microcomputers. Harbour Freight sells this $20 device that beats all the fancy digital testers unless you spend 5 figures.

100 Amp, 6/12V Battery Load Tester

Amazing deals on this 100 Amp 6/12V Battery Load Tester at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Also, inspect and clean all battery and alternator connections.
Then learn about voltage drop testing from the video below or others on YouTube.

A voltage drop from a hidden condition can compromise starting.
The testing is very easy with a digital multimeter.

Diagnosis and Understanding- Voltage Drop

Even most advanced DIY's and troubleshooters are not familiar with Voltage Drop Testing. This video shows a real life example of how lack of knowledge of thi...

www.youtube.com

And welcome to Ram Forum.

.

 

[RoyMunsen]

https://www.justanswer.com/dodge/ftk3y-nobody-tell-me-hope-can-does-2012-ram-1500.html

https://www.justanswer.com/dodge/ftk3y-nobody-tell-me-hope-can-does-2012-ram-1500.html

I appreciate this. I wish I could still see the wiring diagram that was uploaded.

 

[RoyMunsen]

BTW, did you load-test the battery or test with a multimeter?

Reason I asked is I went through some charging 'issues' last yr not unlike yours. Bought a new premium battery in the fall of 2024 for a vehicle I have. When I got the batt home it took FOREVER to fully charge up. That should have been my cue to retuen it to the store right then and there! For the first few months the vehicle worked normally. Then started having issues. Figured ....you know, new battery, had been working fine ... the problems were elsewhere. After a lot of wasted time goofing around troubleshooting this and that, I finally did a batt load test. The battery failed terribly. My suspicion is the battery sat low on the store shelf sulfating...for who knows how long? Or was just defectively made. Regardless, they replaced with a new battery and not a problem since.

So it's worth doing a Battery load test if you haven't done so.

But in your case it sounds a lot like a fusable link. Let us know what the solutions is.

I took it to O’Reillys and they did a load test on it. It passed for them.

 

[RoyMunsen]

I'd check it as close to the PCM as possible to eliminate any harness issues. If nothing there and want to avoid dealer...

2010 2011 Ram 1500 5.7L Hemi PCM Alternator Output Testing & Mail-In Repair

This video highlights our PCM repair service for the 2011 Ram 1500 with the 5.7 L Hemi. We demonstrate how we confirm a no-output alternator field driver fau...

youtu.be

This sounds like exactly what is happening. Thanks for sharing this link. I may go this route.

 

[RamDiver]

I took it to O’Reillys and they did a load test on it. It passed for them.

The digital type battery load testers are prone to false positive results. We have seen this scenario time and time again.

The only accurate load test is with a toaster-style battery load tester as identified above.

Have you reviewed the video above on voltage drop testing and verified the large red wire feeding the starter motor?

.

 

[Ken226]

The digital type battery load testers are prone to false positive results. We have seen this scenario time and time again.

The only accurate load test is with a toaster-style battery load tester as identified above.

Have you reviewed the video above on voltage drop testing and verified the large red wire feeding the starter motor?

.

Last year I bought a ThinkCar ThinkEasy battery tester. It's an add-on unit that connects to my scan tool via bluetooth.

It has a battery test, alternator and starting system test functions, and when it finishes the test it generates a report that you can print or email.

One of it's battery test functions is a load test, but instead of a resistive heating element, the scan tool has you to crank the engine while it's measuring the battery voltage. It uses the cranking as the load, for the load test.

I've wondered how accurate it is. I guess the only way I'll know for sure is if/when I come across one of those batteries with a bad cell that tests good but can't deliver any current.

It's been awhile since I used it, but If I remember right, the load test function was under "starting system test".

 

[RamDiver]

Last year I bought a ThinkCar ThinkEasy battery tester. It's an add-on unit that connects to my scan tool via bluetooth.

It has a battery test, alternator and starting system test functions, and when it finishes the test it generates a report that you can print or email.

One of it's battery test functions is a load test, but instead of a resistive heating element, the scan tool has you to crank the engine while it's measuring the battery voltage. It uses the cranking as the load, for the load test.

I've wondered how accurate it is. I guess the only way I'll know for sure is if/when I come across one of those batteries with a bad cell that tests good but can't deliver any current.

It's been awhile since I used it, but If I remember right, the load test function was under "starting system test".

That's a great idea, but I have to wonder if the tester is still using an algorithm to determine the pass/fail qualification based on statistics of the voltage drop.

So the accuracy is very closely related to the statistical sample size and the algorithm used.

As you say, I suppose time will tell. You would think that a flaky cell would impact the CCA and the voltage drop measurement, thus resulting in a failed test.

It has to be much better than the digital load testers that don't apply any significant load, whatsoever.

The method they use for a pass/fail is always a complete gamble, using statistical analysis and nothing concrete.

I wrote most of this knowing that you're familiar with these concepts, but others may not be too clear about battery load testers.

Please keep us posted on the performance of this test set. I would hope this style of tester would eventually replace the crappy digital testers.

.

 

[04fxdwgi]

Last year I bought a ThinkCar ThinkEasy battery tester. It's an add-on unit that connects to my scan tool via bluetooth.

It has a battery test, alternator and starting system test functions, and when it finishes the test it generates a report that you can print or email.

One of it's battery test functions is a load test, but instead of a resistive heating element, the scan tool has you to crank the engine while it's measuring the battery voltage. It uses the cranking as the load, for the load test.

I've wondered how accurate it is. I guess the only way I'll know for sure is if/when I come across one of those batteries with a bad cell that tests good but can't deliver any current.

It's been awhile since I used it, but If I remember right, the load test function was under "starting system test".

Last year used a digital tester on both my boat engines since the big old 454 MAG was sluggish during cranking. Passed with flying colors and a "battery good" display.

Then tested with the toaster. Both failed miserably. 2 Marine batteries aint cheap.

 

[RamDiver]

Last year used a digital tester on both my boat engines since the big old 454 MAG was sluggish during cranking. Passed with flying colors and a "battery good" display.

Then tested with the toaster. Both failed miserably. 2 Marine batteries aint cheap.

I'm looking forward to hearing more about this new type of load tester that Ken is referring to.

Although it must use some form of statistical analysis, by using the starter as a load, it does sound much more promising than what we have seen with a typical digital load tester.

.

 

[Wild one]

I'm looking forward to hearing more about this new type of load tester that Ken is referring to.

Although it must use some form of statistical analysis, by using the starter as a load, it does sound much more promising than what we have seen with a typical digital load tester.

.

Starter creates roughly the same type of load as the old toaster testers do,and his tester is reading the same voltage drop as a toaster tester does.They've been around for awhile,just not as budget friendly or easy to use as the old toasters are.

 

[Ken226]

just not as budget friendly or easy to use as the old toasters are.

Yea. The ThinkCar battery tester is actually pretty cheap. Like, not as cheap as a harbor freight toaster tester, but $60.



Problem is, it's an add-on to the scan tool, so ya have to have the scan tool tool, in order to use it.

I think they may be owned by Launch, or vice versa. The Launch battery tester looks identical, and i've heard that the Launch scan tools can connect to ThinkCar accessories and vice versa.

I have both a Launch, and a Autel bore scope, and my ThinkScan scanner can connect to and work with both of them.

 

[RamDiver]

Yea. The ThinkCar battery tester is actually pretty cheap. Like, not as cheap as a harbor freight toaster tester, but $60.



Problem is, it's an add-on to the scan tool, so ya have to have the scan tool tool, in order to use it.

I think they may be owned by Launch, or vice versa. The Launch battery tester looks identical, and i've heard that the Launch scan tools can connect to ThinkCar accessories and vice versa.

I have both a Launch, and a Autel bore scope, and my ThinkScan scanner can connect to and work with both of them.

Does the ThinkCar tester show test results as CCA?

.

 

[Ken226]

Does the ThinkCar tester show test results as CCA?

.

It shows a bunch of different measurements. The CCA is one of them.

Ill grab the tool and see if I can upload a battery test result here.

Took a little work to print from the scan tool, then to scan back into the PC. The stupid-ass thing will let me email a scan/diagnostic report to any email address, directly from the scan tool, but nooooo, the battery, starting and charging health report only gives be the option of printing.


anyway, I went back into the history and found 1 of each, a good and a bad battery report.

The 2nd one is interesting, because it shows 12.61 volts, but failed the load test with only 380CCA and 29% capacity. The 2nd one, I suspect, would have fooled the AutoZone type battery testers.



The 1st one was a brand new Napa Legend Premium that I had just put in my truck. I was kinda surprised to see a 800CCA battery test as having 925CCA.
this one. the BAT 9894R: https://www.napaonline.com/en/p/BAT9894R

 

[Wild one]

It shows a bunch of different measurements. The CCA is one of them.

Ill grab the tool and see if I can upload a battery test result here.

Took a little work to print from the scan tool, then to scan back into the PC. The stupid-ass thing will let me email a scan/diagnostic report to any email address, directly from the scan tool, but nooooo, the battery, starting and charging health report only gives be the option of printing.


anyway, I went back into the history and found 1 of each, a good and a bad battery report.

The 2nd one is interesting, because it shows 12.61 volts, but failed the load test with only 380CCA and 29% capacity. The 2nd one, I suspect, would have fooled the AutoZone type battery testers.



The 1st one was a brand new Napa Legend Premium that I had just put in my truck. I was kinda surprised to see a 800CCA battery test as having 925CCA.
this one. the BAT 9894R: https://www.napaonline.com/en/p/BAT9894R


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So what you're saying is the old school standby toaster tester is alot easier to use for the average DIY'er

 

[RamDiver]

Thanks Ken.

I appreciate your efforts to post those reports.

They have great details and I'm confident they're much better than the generic digital load testers.

They're a bit more detailed than my 1990s vintage Princess Auto toaster-style load tester.

.

 

[Ken226]

So what you're saying is the old school standby toaster tester is alot easier to use for the average DIY'er

Yea, and cheaper too!

No scan tool needed.