2015 3.8 AWD with Tech Pkg, intermittent no charging.

[Boomer343]

Like a few others I have chased dead battery issues and searched for solutions. I have checked for parasitic drain and cleaned terminals, grounds and used a contact enhancer called Stabilant 22a. Recently I purchased a Bluetooth enabled battery monitor and hooked it up. It's been 2 weeks and battery voltage has been stable and charging is in specification.
Yesterday though there was a change. After a cold start with no issues the monitor showed no charging was taking place and the battery voltage was slowing dropping. There was no check engine light or any other warning light.
I continued to drive and monitor. I varied the revs, speed with no change. It wasn't until I switched the headlights on that the system showed a 14.5 volt charge taking place. Lights off, back to no charging. Lights on charging again. It was about a 12 minute drive until I shut the car off at my destination. 10 minutes later I started on my return trip and the same scenario played out but I was getting the occasional voltage spikes over 15 volts with the lights on. It wasn't the smooth charging graph I had seen in the past.
I left the vehicle overnight and today when starting and during the hour long round trip with 3 start/stops all was normal.
2015 AWD, 3.8 with Technology Package and 51,000 km or 32000 miles.
Any thoughts or direction? I'm out of warranty and don't have much faith in my local dealer. I can trouble shoot and have a graphing multimeter and the repair pdf but no wiring diagrams.

 

[EdP]

Like a few others I have chased dead battery issues and searched for solutions. I have checked for parasitic drain and cleaned terminals, grounds and used a contact enhancer called Stabilant 22a. Recently I purchased a Bluetooth enabled battery monitor and hooked it up. It's been 2 weeks and battery voltage has been stable and charging is in specification.
Yesterday though there was a change. After a cold start with no issues the monitor showed no charging was taking place and the battery voltage was slowing dropping. There was no check engine light or any other warning light.
I continued to drive and monitor. I varied the revs, speed with no change. It wasn't until I switched the headlights on that the system showed a 14.5 volt charge taking place. Lights off, back to no charging. Lights on charging again. It was about a 12 minute drive until I shut the car off at my destination. 10 minutes later I started on my return trip and the same scenario played out but I was getting the occasional voltage spikes over 15 volts with the lights on. It wasn't the smooth charging graph I had seen in the past.
I left the vehicle overnight and today when starting and during the hour long round trip with 3 start/stops all was normal.
2015 AWD, 3.8 with Technology Package and 51,000 km or 32000 miles.
Any thoughts or direction? I'm out of warranty and don't have much faith in my local dealer. I can trouble shoot and have a graphing multimeter and the repair pdf but no wiring diagrams.

Alternators have the voltage regulator built in. While it seems a bit odd, the load of the lights may be kicking in the circuit for proper charging.

There are some good shops around that rebuild starters and alternators; Look for one near you and see if they can check it out for you..

 

[Suburbazine]

If you're seeing voltage spikes and intermittent charging that isn't smoothly stepped in and out, you most likely have an alternator issue. The voltage regulation is controlled by the PCM, with charge profiles dictated by the BCM (not the alternator). These profiles are designed to most optimally (and with the least obvious ramping) raise and lower the battery voltage to both increase fuel economy and maintain even performance of lamps and motors.

If you're seeing spikes to 15v or higher, that means that the PCM is demanding more output from the alternator but not getting any (until it ramps to that demand level) which indicates a likely issue with either the field windings or possibly the diode pack is failing.