not your average charging system problem...

[JimmyDiesel]

My 92 is intermittently not charging. The intake heaters, tach, cruise, a/c, speedo are working all the time - even when the truck is not charging. The check engine light is on when this condition is occuring. The pcm has a "41" code stored. This is 'gen field not switching properly' . Does anyone know what this means? Is this an internal problem inside the computer it self?



My understanding of the system is... the cumputer sends a negative signal to the alt field relay, when it see signal from the crank position sensor. I am not sure of all this because I don't have the fsm yet. any help would be greaty apprieciated.



-jimmy

 

[kad]

JD,



I recently spent a couple weeks scratching my head with a similar prob on my 90. 5... I realize that yours has the pcm and mine does not... but check the altenator wires. Mine was vascillating between 10 to 13. 5 or so on a handheld voltmeter. Now, bear with me cause I'm electrically challenged... On my alt there were two wires (paired by a plastic housing) attached to the pass side of the alt... very flimsy screws & nuts... anyway one of the nuts had broken off at the base. The paried wires were stiff enough to hold the broken screw in place thus giving intermittent contact. I had to pull the alt apart and disassemble - I'll call it the "screw mounting base" - (another cheesy piece of plastic with the two screws 'pushed' into it). I then raped the same piece from an old spare alt and mounted it on the new alt... no more intermittent problems. My prob was probably a "one-off" but it might be worth a check...



Cheers

kad

 

[EZeis]

Code 41 means an open or short condition in the field control circuit. I would remove the wiring from the alt. and check the ohms on the two field studs on the alt. Then check for a short to the alt case on each stud and also between each stud and the battery stud. Also the auto shutdown relay (ASD) is in the field circuit as well.



Earl