A couple days ago my battery warning light flashed on in my '99 Alero for a minute or two…I hadn’t left my lights on or anything like that…well, last night as I was driving my car and just about every light started flashing and the headlights started dimming…the interior lights went dim and by the time I pulled into my parking spot just about every electrical feature of the car was nonfunctional. This morning the keyless remote entry barely worked and the car, of course, would not start.
So the question is, (based on what I’ve said here) does this sound like a typical old, dead battery breathing it’s last in the winter, or more like a fried alternator that is allowing the battery to drain down to nothing?
DO NOT DISCONNECT THE BATTERY WITH THE ENGINE RUNNING. IT CAN DAMAGE THE ALTERNATOR AND OTHER ELECTRONIC COMPONENTS.
What you’ve described is a very typical symptom of a failing alternator. It’s not impossible that there’s a battery problem, but the symptoms aren’t what I’d expect of a bad battery if the alternator were working. The alternator and battery can both be tested, but the battery needs to be fully charged to properly test the alternator and to get the most meaningful results from testing the battery.
Alternator is stone dead. Sorry about that. AC Delco alternators are unmitigated crap and one of the few remaining real flaws with GM cars (well, aside from the inexplicable inability to offer sporty suspensions and manual gearboxes).
See if you can get an alternator from any other brand. If you’ve got a junkyard nearby try to find one of similar capacity, size, bolt pattern, and wiring on some other car. I believe that the Hitachi alternator used in old Subarus fits a lot of GM cars; take along your alternator and see if that’s the right one for the job here.
That happened to our car a few months back. The dealership replaced the battery and pronounced their obligations under the warranty satisfied, despite our misgivings. It happened again a few weeks later. Once we got them to do a proper check (Words of Power: “Lemon Law”), it turned out to be a bad alternator.
A lot of times when the alternator goes bad you end up draining the battery to the point where you chemically destroy the battery also, so don’t be too surprised if you end up replacing both.
I second Gary T’s warning about disconnecting the battery. You might be able to get away with it on an older car (like from the 1960’s) that has a simpler electrical system, and even then I probably wouldn’t try it myself, but a modern car can be seriously damaged by it. Most cars rely on the battery to do a bulk of the filtering, so without the battery there you are going to get some very wild voltage swings.
Our Safari minivan did this a few years ago. Turns out a diode in the alternator went bad.
And then I got to wondering… before this happened, my wife had (accidentally) left the lights on on two occasions. Each time it drained the battery. Could the deep discharges have overheated the diode in the alternator? Or perhaps the deep discharges caused the battery to pull too much current when the battery was “fully” charged, thereby overheating the diode? I don’t know. But I’ve always wondered if the battery “took out” the alternator…
Quite possibly. Alternators are designed to top up a battery’s charge from normal drains, not to charge a battery that has been significantly discharged. The amount and length of charging involved when an alternator tries to do that is very stressful on it, and can certainly shorten its life.
A 2nd (or third) about this. disconnecting the battery with the engine running can cause the voltage to spike wildly which can fry electronic control units in almost nothing flat. The battery acts like a shock absorber for the electrical system, and dampens these voltage spikes.
Yes, yes, yes, and YES.
I’m not 100% convinced of this, but it is of course possilbe. As you mentioned the alternator is designed to “top up” or trickle charge the battery over and above what the current is needed to operate the car. What would be the difference between running the alternator with a nearly flat (but rechargeable) battery, and driving with your head lights & heater on with a fully charged battery? Both impose considerable loads on the system.
IANAEE, so I am probably over looking something obvious here…
