Check Charging System...Before I rebuild Alternator..Ideas?

[supraraleigh]

The car I am working on is a 1999 Oldsmobile Aurora with 107k miles.  I am trying to avoid the trap of changing out the alternator in vain.


I have read many posted threads about the Check Charging System issue on the Aurora. Many have ended up replacing the battery, alternator, ground wires/points, thermistor, fuses etc. However, so many of these posted threads end up with no resolution to the issue. Whether the issue was resolved and not reported or the car was just given up on and thus the issue became mute, many of the threads are incomplete.

I will continue to report on my issue until it is resolved and I will post how it was.


I am getting the Check Charging System on the display. The voltmeter on the display will read at most 12.5 with the battery charged.  Then, with the engine running, it will steadily drop as the car is only drawing electical power from the battery. I have put in a fresh group 78 battery instead of the OEM size 79 because that is what Walmart had. I  was able to get a slightly used one that they had on a small little rack full of various good used batteries. I think Walmart just started doing this. But, it only has a 3 month warranty. It was just $33 which is alot less that what the group 79 batteries are currently selling for - $180+

I have check the fuses and cannot find any that have blown.  Perhaps I have overlooked a potential culprit blown fuse. The alternator pulley is being driven by belt as well.

I have removed the thermistor. At room temperature is reads 1.58K ohms. According to what is read on this site, 1.68K is the target number. I then wrapped the thermistor with aluminum foil to keep it water tight and submerged it into a glass of cold water. The resistance reading then climbed to 1.8K+ ohms. With the thermistor still disconnected, i started the car but still have the same issue.

I reconnected the thermistor and then started the car, and still get the Check Charging System message with volt reading around 12.5. 

So, before I go through all the trouble of removing the alternator and replacing it, as so many others have done and it did not solve their issue, what am I overlooking here?

[Marc]

Have it scanned. Guesswork on any Aurora is very difficult.

[RCA1186]

Well I would not trust that battery to start. Also the group 79 battery has the proper vent tube attachment which is essential for placement under the seat. At least from what I'm reading. Group 79 also tends to be stronger.

I would get a multimeter and check voltage at the alternator and at the battery. You can also have the alternator tested at most parts stores, if you want to go through the trouble of taking it off.

[AuroraGirlFromMars]

your cs144 has a S terminal, does the thermistor go inline to this? because what you did by removing the sense wire which was temperature adaptive because of the fact the battery is not in the engine bay and that means the charge doesnt have to plan as if the battery is in underhood temp (temp increases the voltage needed... drops or it goes up, i forget!)

If that is true, what im saying, (a diagram will tell you if the sense wire is being used for this)Then your alternator is outputting 13.5-14.5.. at the output stud.

All it takes is a crusty junction connection or some old OE charge wire being a little corroded and have some voltage drop that by time the battery is getting the feed its 12.5 which is not enough. But I also dont know where the feed for the voltage indicator is. Lol.

[fatcity]

My 99 started doing the same thing .  Fully charge battery .  Drive 1/2 hour  back on charger , now at 1/2 charge .   Took car to repair shop , they don't know what's wrong  2 weeks later ,  getting vague answers

[elk]

Im Having the same thing again after like more than a year. At that time I’ve had a “thing” made which forced the computer to turn on charging - this was due to the fact that there was this signal missing and a wholly working alternator was not charging the battery.

Unfortunately I do not remember how was this done and what was the final fix. But… the original problem miraculously returned a month or so ago.

I have the car being scanned one cable at a time to find where is the reason for this fault and it is taking ages… poor we