My check engine light came on a few days ago, and there is a DTC 41. It is charging at 12.47 volts and no amps regardless of load or rpm. I dont want to buy a 208$ alternator if the problem is in the PCM. Can I divorce the alt from the PCM while still on the truck? Any other ways to test? I have checked all fuses, PCM pins and wiring. I would sure appreciate any imput.

 

Hello?? Anyone there?

 

I had same sorts of issues... Although my voltage meter would drop slowly and then fall completely on its face and I would get trouble codes and check engine lights along with Check gauges. After two days at the dealership and them following all of STARs recommendations they determined it was an alternator. I would buy it and swap it out, if it doesn't work, then move on to the next problem, but I would almost bet it is the alternator. I had to replace mine, I had to replace one on my Bro's truck as well.

 

I have rebuilt a couple GM alternators and the occasional ford.....Is there an alternator rebuild kit available for these trucks?

Tony

 

Not a kit but the main parts that go bad
http://www.fostertruck.com/alternators.htm

 

That is exactly what mine is doing, it is just loosing voltage slowly. As long as I dont have lights, radio, blower, etc on, it lasts a while. Otherwise it just falls off. I will try an alternator today. Or maybe rebuild it, never tried that before!

 

Test the alt. , with a load tester connected , eng. running , disconnect the small wire on back of alt. this is what the computer puts a variable ground to to get it to charge , then ground it for a few seconds [ this will full field the alt. { over work it , if left for much longer }] , then you'll know if the alt. needs work , you can also , take to some parts houses to check .
If its good then [ I've seem then with bad brushes & connections work intermittently-thats why testing in truck is best ] look at battery connections , pos. & grds. , fusible links , wiring to & from alt. & computer .
I had one that after looking for bad connection , it started working , 2 yrs. later its still working , never did find the bad connection .

 

On the alternator you have a large wire and two small wires connecting. Disconnect the two small wires, either a plug or two studs. With the engine running, connect one of the terminals on the alternator to the battery positive. Connect the other to ground. If the alternator is good it will go to full charge and above. If it is bad it will do nothing. If the alternator is good, the problem is in the wiring or pcm. There is a fuse to check in the box, it is a 140 amp. It can be blown while changing the oil filter...

If the pcm is bad do a search on this board and you will find a diagram on how to hook up an external regulator and not use the pcm. It will run fine that way.

 

John, I hate not finding a problem like that, but if it works, oh well. I tested the alt the way suggested, turns out alt was bad. I get a pretty good price at the parts house so I just bought new. Now charging at 14.3 and good amprage. I'm glad to know how to divorce the pcm and alt for testing, thanks so much.
Haulin in dixie, how can you blow the fuse while changing the oil filter? Thanks for the help!!

 

Using a metal filter wrench or large pump pliers to remove the filter or what ever tool, it is easy to hit the large terminal of the alternator, taking out the main fuse which disconnects the power from the alternator. Also hard to find one, especially at night when you have to run the truck in the morning. Now how do I know that?