hey all,
my GEN light comes on and dash panel voltage guage is reading around 12 at idle and driving. i checked batt voltage with it off and they are at about 12.2 and then down to about 12.0 with engine idling. did a trouble code test, got 12 and 47. checked my batt connections and they are good. anyway to know if my alternator is bad or if it's the pcm? my book (haynes) is telling me to take it to a shop.

 

Mine did the same thing when the alternator crapped out. Didn't hardly give me any warning either. Sorry for your luck if that is indeed the problem, those things are expensive!

MIke

 

You may be able to replace the brushes and save a few bucks.

http://www.fostertruck.com/alternators.htm

 

The alt may be your problem but I had that same problem with mine a while back and it was a bad connection, cleaned everything up good and gen light went off, this may not be your problem but it wouldn't hurt to check your connections. I would HOPE it was the alt instead off the pcm$$$$

 

Definately your alternator...

if both batteries are good, and all of your other pcm controlled functions work well, then it would be your alternator. MY pcm failed and it was overcharging, THAT is when u start to worry...

Rick

 

It is not definately anything until you test it. Pull the connector off the back of the alternator and you should have two small connectors. Hook one to the battery and the other to a ground. That is on the alternator pins with the wiring disconnected and the large charge wire still connected. Does not matter which is which. Start the vehicle and check the charge. If the alternator is good it will charge up to 16 volts or so. If it is bad the charge will still be down.

If the charge rate is way up on the test you need a new PCM or add a regulator for $8.00. IF it is still down you need an alternator.

 

ok, just put new brushes in and no luck. GEN light still comes on, dash guage still reading just under 12, verified by voltmeter. charge at batteries is now 11.6v. so now do i replace the whole alternator? or should i take it in at this point? otherwise it seems to be running fine.

 

ps. didn't quite understand that procedure by Haulin in Dixie. so disconnect only the wiring connector held on to the two small pins by i believe 7mm nuts? then connect one pin directly to a battery (pos terminal right) and the other to a ground? and doesn't matter which is which? can i use jumper cables to do that? then measure the voltage to the battery? by the way, i measure the charge form both of those pins at idle, one read about 11.6 (right where the batteries were at) and the other measured like .43 or so, very low. i believe it was the upper one with the bigger charge?

 

Hes saying to pull the connector off that is connected to the two pins on back of alt. Then hook up the wires to the posts on the alt. The alt should show full charge to about 16vdc. If you get this the alt should be good and you have another problem. The voltage regulator is part of the pcm. Everything in the pcm can still work even if the voltage regulator part goes bad.

 

"Then hook up the wires to the posts on the alt"

which wires?

 

A positive and negative from your battery. A couple of alligator clip test leads work for me.
It doesn't matter which goes where, they are interchangeable.
The two small stock wires remain disconnected, the large stock wire remains connected.

 

ok, let me sure i have this right. sorry i'm being kind of dense, i just don't want to fry anything.

1. disconnect the small black plastic piece with the two connections to the two small pins on the alt. leave the other heavy (ground?) wire attached.

2. run two test wires, one from each pin of the alternator to the battery. does not matter which pin connects to which battery terminal?

3. start it up and check to see if there is a charge running through the test wires? should be around 16v +/-?

if charge is low, replace the alternator,
if it's ok, get an external voltage regulator?

 

You got it

 

many thanks everyone for all of your help. i ran the test and found the voltage from my alternator to be 11.6, which is exactly what the voltage left in the batteries is. so it would seem that my alternator is just plain dead! is that normal? i wonder what wore out...

 

Brushes or diodes.
My experience with alternators is when they go it's instant, no warning at all.