ltboltman

Posted here the other day on location of the PCM and probably should have expanded the problem...

1. "Gen" light came on the other day and batt has been discharging- I've been charging battery to drive to work and short runs
2. Alternator will fluctuate, sometimes showing a 10 amp charge, other times zilch.
3. I pulled the alternator and autozone checked its output at 14 amps with a thumbs up.
4. Based on what I have read from other posts on subject, alternator regulated by PCM and would require replacement in this situation??
5. If the PCM needs replacement, is this a dealer only item$

Thanks for info

vzdude

First off......fill out your sig. so we know what you are working on. Upper left of screen under the user cp tab. Several things can casue a no charge condition, but it sounds like yours is a wiring issue or something being that it is intermittent. Start with your sig.....each generation has its own set of problems!

lmills

does the tach work? A bad CPS will cause the alternator to not charge also.

EverydayDiesel

I had this similar problem a little while back and it turned out to be a grounding problem.

The passangers side goes directly to the block and the drivers side goes to the frame, I would suggest that you clean those, fill them with water, jump them off and give them a good charge and go from there cause it sounds like your alt is fine

ltboltman

LOL VZ....and # 6 1997 Dodge Ram 2500 5.9L, Automatic Trans, 2wd...Yes the Tach works.......been a real tough week

EverydayDiesel

You should put it in your sig....click on USER CP then click on EDIT SIGNATURE and put that info in there

ltboltman

roger that, Thanks

TallTom

check your relay bank on the drivers side front fender. It has a purple alternator fuse. Its a dealer only part. I shorted mine out when changing my oil filter with channel locks. It will keep the alternator from charging.


TallTom

ltboltman

Everything checked so far (fuses, tight fittings etc.); on the way to work tonight the amp guage showed about 10 amps and then slowly went to 0.

EverydayDiesel

did you clean the grounds with a wire brush?
Mine were tight but had so much dirt and grime between the connector and the metal that it wasnt making contact causing my batterys to not charge.

vzdude

Sounds like the brushes are worn out.

ltboltman

yes, the grounds are clean and tight...the Autozone alternator check showed a "pass" on all the tests performed on the alternator-so taking this as fact, the alternator is functioning OK...something in the charging system, other than the alternator is at fault and as stated, the connections are clean and tight...one thing that may be just coincidental, was that the gen light and this no charge event started after I had hooked up my trailer plug to the truck...but all the trailer lights still work...even with poor battery connections, the amp meter would still show an output right?

EverydayDiesel

Listen to this guy! Hes been right 100% of the time with my 2385206 different problems.

ltboltman

wouldn't the alternator have failed the autozone alternator run-up test?

vzdude

It will run awhile until the brushes overheat I am guessing. The only other things could be the pcm, or wiring somewhere. Have you checked the batteries with a voltmeter while the guage is showing low? If it is actually low, you'll need a scan tool next to see what the computer is seeing. It commands the alternator to charge. It is only as good as the info it recieves. You could have autozone check the alternator for an more extended period.........that may show it. They would need to run more of a load for a longer time. There little "automated" machine may not have the capability to do that. The one I have access to will let me add as much load as I want for as long as I want . Old antique machine, but it works! I have seen VERY few pcms go bad as far as the charging circuit. Anything else I can help you with, let me know!