Well, when I first started having problems, it was well over 105 degrees here every day. It's now in the 80's. A/C on or off, heater on or off, it makes no difference in the alternator performance.

 

Seems like some sorta single issue then. I mean a new alternator and battery - still have the issue. And I did not read back, but I assume no alternator light/battery light? So that still means things have to fall back to the management system as it seems to think both are fine and its "trying" to manage charging.

 

Other than when the voltage drops extremely low (around 11.5), I've NEVER gotten a single warning that anything was wrong. I finally added my own volt meter directly to the battery so I could monitor it as I was tired of it leaving me stranded.

I took it for a drive tonight. It started out around 13.5 after a few minutes it dropped to 13.0 and stayed there for a long period of time. Eventually it dropped to 12.5. Oddly enough, it would drop down to 12.2 and once 12.1. It would hover around 12.3 with an occasional bounce up to 12.4 and 12.5. But this has been the longest trip in several weeks. It appeared to have a slight bit of charging the entire time. When I came to a stop and turned it off, it dropped to 12.2 with the dome light on. So, I can only assume it WAS in deed trickle charging while I was driving.

I remain baffled!

 

Check the connections behind the ATCM

 

It might be worth bypassing fuse f17. Phil

 

Fuse F17 is for the fuel injectors?

 

Doing a little on line research tonight. Remember that everything works fine for about 10 minutes, then gradually the charging tapers off until to critically low voltage. But, for the first 10 minutes it charges fine. I stumbled into this little gem in an online repair manual. It won't let me copy and paste the entire section, so, here's a screenshot of what caught my interest. It's the 10 minute part that has me intrigued. I don't have time tonight to research the entire article, but the 10 minutes has my attention. Going to look into it further soon, busy week at work. Anyway, here's the screenshot.......

 

Ok, let me get this straight. I apologize as I have not followed this thread closely.

There are absolutely no issues with your vehicle except the voltage reading seems low?

 

May seem like a weird question, but does the radiator fan run all the time?

I recall that a bad alternator causes the fan to run as it messes with the ATCM control head which causes the fan to stay on. (one sign of a bad alternator). Do you have another ATCM to swap in to see if you have the same issues? Also look at the ambient temperature sensor.

Remember there are a few things that affect the charging system not just the battery, fuses and the alternator. It is not all basic connections, it does involve logic from a few computers as well. Also it takes the outside temp into account as well. The hotter it gets the less it charges.

For what it is worth I guess.

Jeff

 

Were you able to find the cause? I am having an intermittent voltage issue too and both battery and alternator tested fine...