Engine/Transmission (1994 - 1998) Alternator problem

[MatthewPark]

Alternator problem? code 41...

My truck threw a check engine light today, but not a gen light. The code was #41, "An open or shorted condition detected in the alternator field control circuit. "



Starting my truck up, volts are at 14 on the gauge and a real

voltmeter. About 3 minutes after driving, the volts drop to 12 on the voltmeter. I've searched and read about a few problems, but they all seem to involve the "gen" light. Is there something I should check or something that is common that I haven't found?

 

[WDaniels]

If you voltage drops to 12 after a few minutes, it is not enough to charge the battery. You need at least 13. 25 volts to throw any kind of charge into the batterys. It sounds like you have a loose wire connection or a break that opens up when it gets warm. Also I believe the voltage regulator is in the Alt. It may be going bad also. Drive it to your battery checker outer place, remove it while it's hot and have them check it out. These are things I know that you know already but figured I would reiterate it anyways. If you need a new alt, I know a place were you can get a 200 amp for about the same price the "Dealers" sell for. (never priced one from the "Dealers" tho so it may be cheaper. )

WD

 

[Extreme1]

The voltage regulator on a '94 is in the PCM. How many miles are on the truck? I had the brushes wear out on mine about 5 years ago, new brushes and it's still going. Do take it to a shop and get it checked.

 

[MatthewPark]

The truck has 310K on it.



I took the alternator off and had it checked, and it checked out good. I put it back in and drove it around quite a bit, no CE light, and volts were right at 14. I don't know if I had a bad connection at the alternator or what, but I can't reproduce the problem now.

 

[MatthewPark]

Well, today when I started it, volts were at 14. Shortly after that, 12. 12 miles into my drive, they went back up to 14. There was no check engine light or gen light at any time.



It looks like this is going to be a pain to figure out.



Would it be harmful to throw a buddie's 94 auto ECM in my truck? I figure if I had that thing ready to go when I am experiencing my problem, I could eliminate that as the cause (and leave me with the alternator itself. )

 

[PUMPERDUDE]

I had a #41 a few months ago... . Changed altenator ... Problem gone. .

 

[MatthewPark]

That's the kind of information I was looking for. You had the same exact problem and one single thing you replaced fixed it.



I am assuming it's the alternator. With the problem being intermittent, though, I'd like to make sure I put my money in the right place.



Next time it happens, I am going to jump the exiter wire, and that should tell me if the ECM is the problem. If the ECM doesn't turn the alternator on at some times for whatever reason, I should know by testing this way.