• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

code 41 alternator field fault

bigdumbfun

NAXJA Forum User
Location
belfair, WA
I have a '93 XJ with the 4.0L. About two weeks ago I got a check engine light. Cycled the key once and it went away. It is starting to happen more often now. Maybe not coincidently it has been quite abit colder than usual in the NW. About 20 degrees. The guage upon cold start up reads around 12V and stays that way for 30-60 seconds. It then suddenly jumps to aroud 14V. You can hear a slight change in pitch from the engine bay. All is well.

The code check from cycling the key gives me a 12, 41 and then 55. I know 12 means the battery has been diconnected and I know that 55 means no more codes. I don't completly understand the code 41 though. I took it to Autozone and had them check the alternator. It's fine of course. Maybe I need to leave it there overnight and have them check it in the morning when I first start it up. The belt is a few months old and has good tension. the battery is about a year old and was tested also. Stong as an ox.

I have done a search on this and have found others with the same symptoms, but no exiting conclusion as to what the solution was. Why is evrything fine after a minute? I am not really clear on the regulator part (internal or external). What else could it be? Is this going to get ugly or do I just need to swap out the alternator?
 
I have a '93 XJ with the 4.0L. About two weeks ago I got a check engine light. Cycled the key once and it went away. It is starting to happen more often now. Maybe not coincidently it has been quite abit colder than usual in the NW. About 20 degrees. The guage upon cold start up reads around 12V and stays that way for 30-60 seconds. It then suddenly jumps to aroud 14V. You can hear a slight change in pitch from the engine bay. All is well.

The code check from cycling the key gives me a 12, 41 and then 55. I know 12 means the battery has been diconnected and I know that 55 means no more codes. I don't completly understand the code 41 though. I took it to Autozone and had them check the alternator. It's fine of course. Maybe I need to leave it there overnight and have them check it in the morning when I first start it up. The belt is a few months old and has good tension. the battery is about a year old and was tested also. Stong as an ox.

I have done a search on this and have found others with the same symptoms, but no exiting conclusion as to what the solution was. Why is evrything fine after a minute? I am not really clear on the regulator part (internal or external). What else could it be? Is this going to get ugly or do I just need to swap out the alternator?

There have been quite a few recent posts that the PCM controlled alternators have been testing GOOD at the chain parts stores when they are in fact BAD. If you don't have a good alternator shop around try taking it to a real shop for testing.

41 Alternator Field not switching properly Alternator field is not switching properly in response to PCM regulator signal
It is telling you that the alternator is not responding to the command from the PCM to charge.
 
Check all the grounds specifically the one running from the alt back to the block under the ignition coil. I had that same code on mine a while back and after checking everything the ground under the coil was loose and the ground from block to firewall was loose as well.
 
I'll check the ground later today in the daylight. Wouldn't be able to get it to a shop for a week or so. I am not going to hurt anything driving it this way am I? I could drive my old Toyota truck but I'd rather not.
 
I'm pretty sure all you'll do is maybe run your battery down. Could be wrong on that.

Keep an eye on your GEN warning light and your battery voltage gauge, if either does something it shouldn't, park it, keep the engine running, and measure the relevant voltages (field coil, ignition output, frame ground to engine block, battery, and battery negative to frame) then make sure it's still doing it and post the results up here.
 
this has been going on for about a month, so I think that the battery is safe. Charges fine after less than a minute. I'll just change out the alternator in a couple weeks when I have some time. I just wanted to make sure that I wouldn't risk damaging anything until then. Thanks. I'll post wether or not this fixes the problem when I do.
 
I could never find an end to this story when I was doing a search on it. Lots of similar symptoms though. I replaced the alternator yesterday and so far the problem is gone.

A couple of notes though....

1. This started out hit and miss and became increasingly regular over about 6-8 weeks. The time it took for the needle to go from 12 to 14 also took longer over time. But it never did hurt anything else.

2. I thought that this may mave been aggrevated by the cold weather at first. Apparently not, as it didn't get any better when the weather warmed up.

3. I did check all of my connections and battery cables for corrosion and tried the old alternator again. That didn't help either but they all looked acceptable to begin with. But it was worth a shot.

If I do start to have problems again (and this wasn't the fix) I will post again. Thanks for those who helped me.
 
Back
Top