Engine/Transmission (1994 - 1998) Code 1388 & 1389 Alternator Woes

[wiederhold]

I've read through a lot of the articles about alternator issue and there is some great info! Hopefully my question wasn't already covered in a thread that I might have missed. My truck is a 98 12 valve automatic 4X4.



Long story short is that I don't have any voltage at the + field connector and the ground side is okay. This after having brushes installed while on a trip to Baja California. After the install, the system was charging but we noticed that all the lights were fluttering. The auto electric guy that did the work on it decided he'd better check that out and subsequently burned "something" out. To get by I'm feeding the positive side of the field with a 12 volt switched line and that has been been working/regulating. (Which leads me to believe that the regulator in the PCM is okay. ) By doing it that way I do have alternator noise on my comm radios which wasn't there before. So I really would like find out where the "missing" 12 volts issue is. I put a tone generator on the hot lead at the alternator and found it to have continuity all the back to the PCM and swapped out the cut out relay (ASD), still no joy. From there I ran the codes and came up with 1388 & 1389, both of which point to the ASD and no current from the PCM. And yes the tach is working. Only other oddity is the speedo does jump around a bit, even when sitting still.



I know about being able to install an external regulator and don't really have any problem doing that. Just that I like it all to work as it did before. Any information would be greatly appreciated!

 

[K5IP]

If you did not have 12V on the field, the ASD was a good choice. Unfortunately not the right one. The ASD is powered by the PCM, based on inputs from the engine speed sensor. Unless you have made an error, that leaves the PCM. I'd look carefully at the input to the ASD and trace voltages, or lack thereove all the way back to the PCM. If still no joy, it might be cheaper to go the external regulator route.

Rog

 

[Howard Durand]

Maybe this is not relevant for your 98. I am looking at a service manual for the 94. Do you have +12 volts on the Distribution Center side of the ASD relay? On my truck there is a 30 amp fusible link or fuse in the PDC that feeds the generator field and the PCM via the ASD.