Why does my alternator read bad?

Asked by Rita Feb 06, 2023 at 01:43 AM about the 2002 Chevrolet Tracker ZR2 4-Door 4WD

Question type: Maintenance & Repair

I have a 2002 chevy tracker and Im going through alternators like crazy.  The
parts store checked the last one and it reads good.  I put it on the car and it
reads bad.  I have replaced the battery, alternator, belt, battery cables and
terminals, checked all fuses, changed the ground wire.  What could be causing
my issue?

7 Answers

38,895

Don't make a new alternator charge a low/dead battery that may account for one , The alternators may be junk out of the box look for AC delco OEM parts , How are you " reading " the out put of the alternator ? Those other parts didn't seem to solve the problem you could have bought a multi meter for the money you spent .

307,195

This vehicle has a computer controlled charging system, so the entire system needs to be checked intact not in sections, find a good independent shop in your area that can the this. This is not the first time I've heard of this happening and it turns out to be the computer itself.

1,800

The plug connector should have one wire that is 12v one should be ground to pcm and dash light, the other should have 7.0 volts the 7.0 volts is the exciter wire to activate the diode pack and create charge upon start signal is sent to pcm, pcm then cuts ground to dash light turning it off. Pcm as previously stated may be part of charge system (regulation) check the main fuse and battery connections there are two parts to positive side w an inline fuse or in fuse box under hood.

I am using a multi meter and I also have a diagnostic code reader. The multi meter reads 11.98 on a good day. It has a new battery. It isn't dead. I also carried the new alternator and had it tested at the parts store and it reads good on their machine. I'm not worried about the money I have spent on parts, I'm stumped about what is causing this issue.

307,195

11.98 volts is not enough, that reading is battery voltage and that tells me that the alternator is not being turned on by the computer. Plus carrying in an alternator for testing is not a good idea as it only tests the component not the whole system. Does the ALT light turn on when you turn on the ignition? If it does great, if it doesn't then you need to replace that lamp cause it is part of the exciter circuit for the alternator. I still think you need to go an independent shop and have it fully tested. Do you have any codes?

1 people found this helpful.

i know it should read 14 and I had the alternator tested so i would know for sure that the new one wasn't faulty. Yes, the light does come on with the key on. It isn't throwing any codes at all. The check engine light doesn't stay on.

307,195

Sure sounds like the computer has lost the charging programming.

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