I have searched through the forum but could not find anything specific with my situation.

I have an intermittent Red triangle "charging system fault" that is mostly on, only occasionally coming off. There seems to be specific conditions that trigger it that perplexes me.

Some background:
-Alternator replaced at 130K, currently at 198K
-Battery replaced 4 years ago (Interstate AGM)
-"cold" battery tests at 12.32V, at running idle ~13.4V, with some additional revs, bumps up to 13.6-14.2V. Leads me to believe alternator behaving as expected. Battery at rest voltage seems maybe low to me?
-Had battery tested at autoparts store, they only checked CCA, which tested as GOOD and 925 CCA (rated for 900). Can it have good CCA reading and low voltage and be bad?
-only one battery, no secondary battery in cargo area
-seems to drive normally, but heated seats do not work (they did work before charging fault came on), everything else electrically related seems fully functional
-checked wheel arch grounds, and they seem intact.

Under hard acceleration, the charging fault will always light up. After driving in more docile manner for 10-15 minutes, light will usually come off. If idling at stop light, charging fault will come on again, only to go off after some minutes of docile driving. It will go through that cycle of on and off frequently, though sometimes the charge fault will stay on with those same conditions.

The trigger from hard acceleration seems like it would point to a bad alternator, belt or tensioner where it might not be getting enough regeneration from the alternator but the voltage test seems to suggest the alternator is good. The belt seems generally tight enough but there is some deflection, though not sure what is normal.

I am leaning towards a weak battery that can never get up to charge fully but a bit confounded by the CCA test showing a good battery. Given the battery is also 4 years, I suppose it won't be the end of the world to replace but also don't want to do that unnecessarily if it is still good, and batteries are typically not returnable.

Any thoughts on anything obvious I might be missing in my trouble shooting?

I think the alternator varies its output depending on what load it thinks it needs to supply, so at idle if its not doing much, then it'll drop its output voltage.

I've read that if its low at idle, then if you switch the lights on, it should bump the voltage back up to 14.5(ish) to power the lights properly. Maybe worth testing varying the electrical load at idle and seeing if the system responds ( like lights on, blower motors etc etc ) V8 or else ...

Thanks for the reply fisha. I did the load test and with the alternator running the voltage does not drop appreciably with a high electrical load, stays in range of 13.6 to 14.2. Is it suppose to fluctuate between a range or stay steady?

I should also mention that it starts very strongly, no hesitation, even in temperatures around -15C.

So I had the Charging System Fault about six months ago, turned out to be the alternator. Funny thing is a few day before the message came on I did smell a very electrical smell, if you know what I mean. I thought it was the car ahead but im gussing now it was my alternator giving up the ghost. You've bought WHAT!!

Update: RR showing to be very temperamental

I plugged a cheap OBD2 scanner with live data ability to monitor the fluctuating voltage. Strangely enough, since I plugged it in, the charging system fault warning has only come on once and quickly extinguished. This has been about 4 days of driving.

What I have found out with closely monitoring the voltage, is that the overnight battery voltage drops to about 11.8-12.2, then drops to about 10.8 during crank and immediately goes back to 13.6-14.5 once the alternator regenerates.

I don't know what to think, other than I seem to have a weak battery but it starts/cranks very strongly, no hesitation which is puzzling. I am inclined to replace it anyhow.

I could be the battery monitor itself giving spurious readings.

I had on my L322, different car but same principle, it was a loose plug on the negative battery terminal, removed it, cleaned and refitted, problem gone.

Tiny thing, 2 pin, thin blue wire, there's a similar wire on the positive terminal but that is a crimp connection.

A. Fuji White / Jet 2012 4.4 TDV8 Westminster

You probably have some codes stored which your cheap OBD will not read....??

If your cheap OBD did do a partial fix, maybe plug it in a few more times, you never know.....

I'd start with the battery, at 4 years it will be a bit poorly and fatties do like a good voltage...

Good luck....  Pete
I now have permission from the boss to use Y.O.L.O. Enjoy life
__________________________________________________
2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-