Alternator buzzing/humming when vehicle is off?

[cjncustoms]

I have a 6.0 vortec in my jeep and when I turn the engine off you can hear a very quite buzz/hum coming from the alternator if you listen closely. If you unhook the wire that charges the battery it goes away. Any ideas on what's causing this? It drains my battery in a day maybe less... Any help is greatly appreciated.

Thanks,
Calvin

 

[SAVAGE]

This might be a long shot but when you turn your ingnition on it sends power to the alternator field so it can run the voltage regulator. Im thinking maybe when you shut the ign. off it is still sending the 12v or whatever to the alternator to run the voltage regulator. Thus making some kind of noise you can hear when the motor is off, and slowly draining your battery. You could try testing the alternator plug wires with a multimeter to see what wires get power when the ign. is on with the motor not running, and see if there is still power when you turn the key off. If there is still 12 volts coming into the alternator (through one of the smaller wires) with the ign off I would guess there is a problem between your ignition switch and your charging system somehow providing power even though the key is off.
I dont know if any of this makes any sense but i hope it helps. Good luck

 

[Bobzilla]

Use a digital ohm meter volt tester and with the key off, check the alternator housing to see if it has voltage, put the ground of the volt meter directly to the battery ground and the positive lead on the alternator housing.

If there is voltage on the housing, the alternator is shorted internally, that would explain the battery drain after a day or so. Take it off and have the bad parts replaced, I believe the diodes may be the cause a short circuit, battery drain.

 

[cjncustoms]

Thanks guys. Got her figured out.

 

[frieed]

And the solution was ???????

 

[SAVAGE]

did you just get a new alternator? don't leave us hangin...

 

[cjncustoms]

Kind of embarrassing for me, but I somehow had the PCM key on power and the PCM memory wires crossed... So the PCM always had 12v and always sending 9 volts to the alternator. Switched those 2 wires around and good to go!

 

[SAVAGE]

Sweet Im glad you got it figured out, especially cool you didn't have to spend any money.

 

[Bobzilla]

that's cool you found and fixed the problem