Hello, I wanted to share my experiences and repair that resolved an intermittent battery warning light on a 2012 Town and Country Touring with a 3.6 VVT Pentastar engine. As this took me quite some time to figure out and was a huge pain in the butt!

I recently started experiencing an intermittent battery warning light with no DTC codes. Some days it would come on and some days not at all! I did several basic checks to confirm the alternator was good (tests below) and all seemed to check out.

Charging System Tests:
Alternator B+ to Batt (+) Term = 0.13 Vdc (should be less than ~0.4 Vdc)
Alternator Housing to Batt (+) Terminal = 14.14 Vdc
Alternator Housing to Batt (-) = 0.017 - 0.025 Vdc (should be less than ~0.2 Vdc)
Alternator B+ to Alternator Housing = 0.025 - 0.030 Vac (should be less than 100 mV) Note this is AC voltage to check for bad diodes!
Alternator B+ to Alternator Housing = 14.3 Vdc
Batt (+) to Batt (-) = 14.1 Vdc

Since the charging system appeared okay, I started monitoring battery voltage while driving the vehicle using a scan tool. The scan tool picture below shows what was happening when the battery warning light would come on . It shows the alternator voltage dropping rapidly, then shooting back up after a short time. My guess was the PCM detecting low voltage and trying to compensate for the rapid drop in charge voltage.



My first thought was a failing PCM module, poor connection or damaged wire. But considering the tests above that didn't seem like the issue. Then looking at the graph closer, it shows voltage dropping to key-off battery voltage (~12.8 Vdc) or the alternator completely dropping out. Thinking it could be a slipping belt, I replaced the belt and tensioner/pulley, but the battery warning light came up again.

As a shot in the dark, I decided to replace the alternator. As I have had issues with them failing in the past on this vehicle and this alternator had about 60k miles on it. After I removed the old alternator, I noticed that the alternator pulley clutch had more slip to it than the remanufactured unit I purchased (Mopar Part No. R4801624AG). A few days after I replaced the alternator, I have not experienced the intermittent battery warning light and it appears the charge voltage has increased from ~13.9 Vdc to ~14.1 Vdc while driving. Which could also potentially explain a loose or slipping alternator pulley clutch.

I plan to tear the old alternator apart, inspect everything and include that in this thread at some point. But I'm leaning towards this issue was caused by a worn alternator pulley clutch. From what I can gather, the clutch was slipping causing the rotor to reduce in speed or freewheel for a short time causing voltage to drop rapidly. Then the clutch would re-engage, PCM would detect low voltage and send current to the alternator field to boost voltage back up.

When I read the service manual, a low voltage DTC will be generated if voltage is less than 11.5 Vdc and a high voltage DTC will post if voltage is higher than 16 Vdc. Based on the scantool readings, the charging system never reached to those voltages. So that would explain why a DTC code was never posted. However, this appears to be another detection mode not fully discussed in the service manual. My issue was fluctuating charge voltage with no DTC code. So apparently, the PCM is monitoring charge voltage and if some threshold is exceeded it will illuminate the battery warning light with no DTC code. Does anyone have information on this mode? I can’t seem to find many details in the service manual.

Whew...well I hope this helps some people in the future and saves them some time and money. I was planning on shotgunning the alternator and PCM module together. But in my case, appears it was a simple worn out alternator pulley clutch. I figure this can be applicable to many different Chrysler products with an internal clutch pulley on their alternators.

Cheers!