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Alternator draining batterys

K

kojo

diesel head
Messages
295
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2
Location
Finland, Europe
One weekend when my silverado wasnt in use for about 3 or 4 days i noticed starter was feeling lazy and started keeping electrical gremlins on eye and i did found explanation: Alternator pulls 0,5 A all time and makes very low butting noise (just like transformer)
So i replaced alternator and same problem continues, it pulls that current directly from battery through that bigger wire, but current goes to 0 if i pull thin wires off from alternator :???:

I checked service manual and those thin wires are going to ECM is my ecm bad or does it need update from dealer? :mad2:

I have to fix this before winter couz all available power is needed when there is no carage and temperature is -30'C :rolleyes5:
 
Somehow your ALT is getting 'energized' through the 'turn on' wires (black/white)... Both of these should be zero volts key off. The charge wire (big red wire) obviously is hot all the time. The turn on wire energizes the field which draws currant; about the amperage your figure states.
 
Try unhooking the 2 plugs from the ECM and then plug the alternator plug in and see if it is still drawing current. If it is then you probably have a shorted or chafed wire somewhere in the circuit. If it doesn't draw current anylonger then I would suspect your ECM has gone out on you and is triggerring the alternator all the time. You could always wire it up manually to get you by for awhile if your ECM is bad.
 
Pull the battries for 30 seconds or more and let all the computers "reset". See if the alt is still buzzing after 5 min to 20 min after reconnecting the wires and turning the engine on and then off.
 
i had to move my truck on yard and when i went to truck now it wasnt buzzing so i took my ammeter (clamp type) and there wasn't any current, i'll check again before leaving to work.
 
Check the wiring harness closely down by the power stering pump for chafes or damage. This is a known point where teh harness can get damaged and caue intermittent issues. Also make sure teh 2 bale connectors for teh engine are fully seated in place and in good shape.
 
Food 4 thought.
As we live in the far north I always go over the tops of my batteries with a soapy damp cloth once a week as they salt the roads here and being salt is a mineral could and would leave un-answered problems.
 
:nonod: Fault has come back...
I measured voltage from that 2 pole plug behind alternator, there was 2 volts when iginition was off, i think it isn't normal and i asked friend to check from his 01 lb7 he got 0,35 volts :rolleyes5:
 
I forgot to tell, problem is solved.. for some unknown reason ECM in that truck keeps alternator energized some minutes after running, but turns it off later, so it isn't draining batterys, but left side battery had dead cell, got new battery (only one) warranty and truck worked until i sold it.
 
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