Stranded code 41 alternator field circuit?

[TheOoz]

Any help appreciated. No charge, code 41, two alternator fuses are okay and the circuit/wires are all okay. Occurred heading up a hill on the freeway. Downshifted to second on cruise control and the dash lights dimmed. Noticed the alternator not charging and check engine light came on.

[layback40]

Originally Posted by TheOoz

Any help appreciated. No charge, code 41, two alternator fuses are okay and the circuit/wires are all okay. Occurred heading up a hill on the freeway. Downshifted to second on cruise control and the dash lights dimmed. Noticed the alternator not charging and check engine light came on.

First thing would be to check the alt brushes. Often that is all that is faulty ~ an easy fix. Not worth replacing alt if its only the brushes.

[Escapable]

Firstly .. the field windings DO NOT HAVE BRUSHES

This error is for the "field windings"

The output from an alternator is governed by the input current in the field windings and this control voltage comes from the PCM itself.
If the connections (2 off - the small wires in the connector) are OK and they have voltage applied to them (to each other, not to ground) then you can use an Ohmmeter to test the field windings, although this may seem ok if they are shorted internaly.
WARNING .. most auto electricians will tell you "never seen one like that".. LEAVE IMMEDIATELY!!!.. this is not a JEEP thing, many vehicles use this method of control and they will tell you to put a "real one" in there.. these are internally regulated and will require additional wiring to the battery.
Now for the WARNING: The jeep PCM will not have control of the alternator and will constantly RESET itself (as it does when it starts up) and some modules like the dash will black out the instruments and beep and .. well.. get the real one fixed before you go crazy ...been there, you don't want it and if you shop around.. it aint expensive.
According to various sites you can get rebuild kits but this may also test your abilities, best to replace or auto electrician.

This alternator control is also possibly one of the reasons "silly" things start happening when the battery starts to age.

[layback40]

Originally Posted by Escapable

Firstly .. the field windings DO NOT HAVE BRUSHES

This error is for the "field windings"

Yes we could read !
& you are 100% correct.
However unless you either know how the control system works to determine faults, that is you have a detailed knowledge of the programs used, it is quite possible that brush ware could cause a faulty output from the alt & show as a field winding error.
It could be a de-lamination of the field also or a diode fault. Brushes are easy to check & in a significant proportion of cases are the cause of other faults. I once had a locust lodge itself against the brushes & the initial advice from an auto elec was that the diodes had failed & I needed a new alt. This was on a Mercedes.

[TheOoz]

Thanks for the responses. The alternator is about 6 months old and is a brand new Chinese made TYC from Rock Auto. It is still under warranty if it is the fault. Any suggestion on how to test it? Just check continuity from the terminals to ground as a start? Anything else?

I installed the alternator myself and knowing it is fairly new I checked all of the wiring on the side of the road. It all looked okay, but I didn't have a multimeter to test it further.

[TheOoz]

New alternator has been dispatched. I will fit it and provide an update!

[Escapable]

Originally Posted by TheOoz

Any suggestion on how to test it? Just check continuity from the terminals to ground as a start? Anything else?

The field windings do not work to the vehicle ground but to each other under the control of the PCM, so you will only be able to test continuity, however there are multiple windings in parallel and any faulty windings (unless shorted) will not show up.