GMC Troubleshooting Questions? Ask a Mechanic for Answers
how long to they last ?
what brands are they ?
are they reman or brand new alternators ?
even thought he diode failed what was it putting out for volts and amps when tested ?
and the amps where good ?
no check charging or batter lights on in the dash ?
are they 100 % sure the batterys volts and cold cranking amps and it was tested for bad cells ? and 100 % sure the battery is 100 % good for amps and for bad cells ?
if that battery is confirmed good with cold cranking amps and volts and it has NO bad cells in it pick up a GM new alternator and install it the Autozone will refund your money and see if this still happens
the odds are there is only 2 wires from the computer to the alternator and they are good and even if bad or the computer was bad it should not cause an internal alternator issue
also keep in mind a battery that had been knocked down to dead over 2 times can never fully bounce back to full cold cranking amps
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bad cables would not cause this
the only test to be sure the computer and wiring from the computer to the alternator is good is most shops have a plug in tester that you unplug the alternator and plug the alternator connector into the tester and look for green lights'
if all green lights its good if any red the wires are bad or the computer is bad
the problem is the signal is sent pulse width modulation which no meters can read
4 to 6 years BUT every time a battery is deep cycled so to say it never will come back they can loose @ 20 % off the top each deep cycle
the computer tells the alternator how much to charge and when to charge v/s the voltage readings the computer is reading off of its input powers so it knows when to charge and how too
i would highly recommend the local GM dealer and just have them test it for you
it will not cost much to be 100 % sure what it is then either have them fix it or fix what ever they say the problem is
how are you making out ?