96 blazerbattery light on

[blazer4819]

I bought a 96 blazer from a woman who took great care of it, all maintainence, kept all the records etc. I drove it home a bout 40 miles and the service engine soon light comes on. The car slill runs fine but now the battery light comes on after a few minutes. If I rev it up to about 2500 rpm it goes out but comes right back on when the rpm drop. I removed the alternator and had a napa store check it , perfect, no problems. Next I put a different battery in, same deal. The wiring looks great, all connections are clean and tight. Where do I go next, the dealer? The car has 160000 miles and is an LT, loaded. Thanks in advance for any ideas.

[MT-2500]

Originally Posted by blazer4819

I bought a 96 blazer from a woman who took great care of it, all maintainence, kept all the records etc. I drove it home a bout 40 miles and the service engine soon light comes on. The car slill runs fine but now the battery light comes on after a few minutes. If I rev it up to about 2500 rpm it goes out but comes right back on when the rpm drop. I removed the alternator and had a napa store check it , perfect, no problems. Next I put a different battery in, same deal. The wiring looks great, all connections are clean and tight. Where do I go next, the dealer? The car has 160000 miles and is an LT, loaded. Thanks in advance for any ideas.

Make sure the different battery is good.

What is the battery voltage reading off and then with engine running?

Pull code for check engine light and post back code no.

[MT-2500]

Somer auto parts places will give you a free charging and starter system check.

[blazer4819]

I don't know, I guess I'll just take it to the dealership and have them check it out. It's just funny that when I rev it up the light will go out. It sure seems like an alternator but who knows.

[MT-2500]

Needs proper testing.

Always have alternotor and battery checked out on truck.

Voltage redings are a have to have to tell what it is doing.

If you can not check them your self find a good repair shop and let them have at it.

A dealer is the highest place to have it repaired.

[blazer4819]

I put my multimeter on the car and it reads 12 volts with car off. I start the car and it reads 14.5 for between 30 and 60 seconds then starts to fall off, settling in at 11.4 volts. Sometimes reving it grings it back up and sometimes not. I don't have a code reader and it's an ob11 so I can't get a code. If I clear the code it stays off till I drive the thing. Anymore ideas? I'm not presently driving the car yet but I need to get it fixed soon as my leaser goes back.

[blazes9395]

This is a alternator problem almost for sure, specifically the regulator circuit in/on the alternator. It is most likly overheating internally and stops working. Its designed to essentailly stop producing voltage if it overheats. Probably the reason why it passed when tested at NAPA, is because it produces the proper voltage for 30-60 seconds, about what they test it for.

Your battery is also undercharged. Before installing a new alternator, make sure the battery is properly charged up.

[blazer4819]

Blazes, thats my conclusion also. I'm going to take it off and stick a new one on this morning. If we're wrong I'm out 130 bucks and have a spare.

[blazer4819]

Well after getting the alternator checked 5 times on 2 different machines and having it come up good every time I replaced it anyway. All good now.

[Rick Norwood]

I had a similar problem many years ago. The electrical system would go totally nuts. The headlights would barely glow, the A/C fan would barely blow enough to feel etc. Then without any notice, everything would come alive, the headlights would look like highbeams, the A/C fan blew like a hurricane, and then shut back down after a few minutes of driving. The Alternator tested good but the internal voltage regulator was bad, it was either on or off. A new Alternator fixed my problem too.

[old_master]

Originally Posted by blazer4819

Well after getting the alternator checked 5 times on 2 different machines and having it come up good every time I replaced it anyway. All good now.

Like MT said, that is exactly the reason for testing on the vehicle. Those machines at the auto parts stores are worthless.