Faulty Alternator

Hi all,

Some time ago my 1994 3100 V6 Grand Am started acting a little crazy.... the brake light, ABS light, oil light, service engine light would start flashing on and off on the dash (accompanied by a clicking under the hood on the drivers side, presumably some relay). The radio would also refuse to work and the display would be a mess. This was a times also accompanied by interior lights going on and off and doors locking and unlocking !!!

This all usually but not always happens when the weather is wet and the car is first started. After 5 mins or so all this craziness stops.

Now, the other day the battery light came on and the gauge was at the quarter mark instead of its usual 3/4 mark. (Sorry I forgot the exact readings)

Around 5 mins later, the battery light went out but a whinning noise has started coming from the area of the alternator. This whinning increaes in pitch along with revs and the batt gauge now reads around center or just below when the car is idling whereas before it was around 3/4.

I used a voltmeter on the battery which gave 12.5V with the car off and around 14.5V with it idling.

Do all these problems point to a faulty alternator and if so, just how easy is it t change on this car as I understand that the serpentine belt cannot be changed without unbolting the front engine mount.

Many thanks for your help.

If you are getting 14.5 volts then the alternator is working. The problem may in fact be the battery cables and the grounds of the car. Remove the battery cables and clean the terminals. Also check the main ground on the car. Finally, if the serpentine belt hasn't been changed in the last 60K miles you really should have it changed since it is probably the cause of your problems.

Many thanks for the replies.

The battery is relatively new and was tested at autozone not long ago and was then fine.
I have taken the cables of the battery and cleaned the terminals, no visible signs of corrosion.
I will try replacing the cables in case of interior corrosion. This may be a problem as the flashing dash lights and door lock problem started after I changed the old battery. The 'alternator' problem has only recently started and may well be a seperate issue.
I am taking the car to autozone today for them to test the alternator and battery.
The car has always started fine, as if there is no problem but the battery guage is reading low and near zero when lights, window heater and heater are on.

The serpentine belt has not been changed in the last 60k miles.
Could the whinning noise be a slipping or worn serperntine belt and the low charge from alternator be caused by the belt slipping and rotating the alternator enough ??

Visibly the belt looks ok and is within the wear indicators on the tensioner.

It was a little strange when the one on my 96' went out last year (leaving me with a 3 mile walk home on a pretty chilly day :shakehead )

Mine started with weird stuff lights going on radio messed up as I tryed to limp it home. Then engine died and wouldn't re-fire.
Strange part was after getting it towed to shop, it initialy tested fine. For whatever reason the mechanic left it running after the check, and another guy at the shop happened to catch a change in sound of engine and suggested another check. Sure enough it had suddenly stopped working right and was putting out low/no voltage. Guess you can't always depend on initial check to determine if its working.

the serpentine belt slipping could be causing your entire problem. Another part of that could also be the belt tensioner losing its ability to hold tension on the belt. This can cause similar issues. I would change the belt and the tensioner to see what happens but I believe that will eliminate your problems.

Thanks all again....

I took the car to autozone today and they tested the alternator.

Results..... initially the voltage output was around 14v then after around a minute dropped to 11v and back to around 13v fluctating around the 2 for a few seconds.
The guy then did a diode test and the alternate failed on this.
His conclusion was that there were some bad diodes in the alternator (also the possible cause of the whinning noise) and that it was giving out some voltage but not working as it should be, especially when heater, lights, radio, rear window heater etc were on, which is true, if I switch all those on the guage nearly drops to zero.

So autozone concluded that the alternator is faulty and I plan on crossing my fingers and replacing it tomorow.

This has been happening around 5 days now, when I initially checked the belt it looked ok and the tensioner was within its 2 marks, but I will check it again tomorow.

The flashing lights on the dash have been happening since I changed the battery some while ago and may be a seperate problem, possible corroded cables has some has suggested.

If I can fix the whinning noise and the charging problem tomorow I will be happy...then I will tackle the flashing dash lights!!

Update.............

I bought an alternator from autozone, and loaned a serpentine belt tool for the tensioner ($25 deposit so costs nothing as long as you take the tool back).

Replaced the alternator, straight forward job, only problems being a stubborn bolt and dropping a socket down under a rear spark plug boot...doh!!!

The new alternator has stopped the whinning and charge is now good, steady and constant no matter what accessories are on !! yeahh !!

The dash lights haven't flashed on and off yet either, but they never did on a reliable basis so it will be a week or so before I know if the alternator has fixed that problem too......I'll keep you posted.

Thanks to all for all your help and suggestions.