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John, Master A.S.E Automotive technician
Category: Chevy
Satisfied Customers: 9176
Experience:  A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
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My 2003 duramax today and the battery light..charging..voltage

Resolved Question:

i started my 2003 duramax today and the battery light stayed on and the message read battery not charging. i replaced alternator and still shpw same message. i have voltage to the alt. but show no voltage when the engine is off or on with either of the two wires that go in the top of the alternator also the guage is showing 12.8 volts while running. all fuses are good.
Submitted: 7 years ago.
Category: Chevy
Expert:  John replied 7 years ago.

Hello & Welcome to JA,


Correct voltage when the engine is running & alternator charging is 13.9 to 14.2 volts at varied amps/

The vehicle computer controls the alternator charging system & there is not suppose to be voltage on the 2 wires you speak of.These are the control circuits from the computer.
I am sending a schematic & you need to check the wiring & make sure the grounds are good.You may have a faulty computer.


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