No alternator output

2002 CHEVROLET SUBURBAN

180,000 MILES • 5.3L • V8 • 2WD • AUTOMATIC

SS21

MEMBER
1 POST

I had alternator tested and passed with flying colors. Battery charged and holding twelve plus volts when not being used. When reinstalled on vehicle alternator still does not have any output. I tested the connector that attaches at the back where it connects to the voltage regulator, seems to be getting proper power from computer. The only thing I did when it began having issues was tighten some bolts on the bracket that holds alternator to the block. It should not have affected anything but the ground side. If I tighten the bolts holding bracket to the block why is it not creating a better ground? Any thoughts on how to restore charging would be helpful. I am at two weeks spending all free time on this now.

Oct 18, 2017 at 8:30 PM

PATENTED_REPAIR_PRO

✓ASE Certified Mechanic
1,853 POSTS

Since it is the PCM that contains the voltage regulator and when bench testing that alternator and it passing the test, because the PCM is not included in that test leads me to believe that the problem just might be with the PCM and the voltage regulator function within it.

Oct 19, 2017 at 7:35 AM

CARADIODOC

✓ASE Certified Mechanic
34,321 POSTS

Voltage regulators are only in the engine computer on Chrysler products. They do that so the computer can adjust target charging voltage for a variety of conditions including air temperature, wide-open-throttle, AC on or off, etc. Other vehicles do this too, but with additional wiring and connector terminals to potentially cause trouble.

For GM's system, start with the basics. Does the "battery" light turn on when you turn on the ignition switch? If it does, the "turn-on" circuit to the voltage regulator is okay. The regulator is built into the back of the generator and is just about impossible to replace, and it is impossible to bypass it like you could on the 1986 and older models. Next, does the "battery" light turn off once the engine is running? If it does, measure the voltage on the large output terminal on the back of the generator. It must be between 13.75 and 14.75 volts. If you do find that, measure the battery voltage. It should be exactly the same. If you find closer to 12.6 volts or less, the generator fuse is blown. On newer vehicles like this, that is a large fuse that's bolted into the under-hood fuse box.

Oct 19, 2017 at 4:39 PM

Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.