Hi,
I recently took my Mazda Protege 2000 in for oil change and check-up. Drive belts were wearing and were replaced too. Next day, after accelerating, battery light came on and stayed on a little while and airbag light intermittently flashed on. It eventually went off, but since I was in the area where dealer shop had worked on car, took it there. They checked it out the next day and said it needed a new battery, as the battery was the original and that they were going to clean up some grounding wires. Couldn't afford to have them replace battery, so took it to Sears. On way back from Sears same thing happened, so I drove it back to them. They looked at it the next day and could not reproduce light situation. After I insisted that they do the acceleration thing, they eventually had it happen. Their thoughts were alternator or computer, as it turns out that more than 12 volts is coming out of the alternator when they simulate this in the shop. They still can't decide between alternator and computer and say they need to test it more until it happens more consistently. I was fed up with them, because none of this happened until after they replaced the belts and decided to take it home for the weekend. It happened twice on the way home. This time it was not after on-ramp type of acceleration. I tried to notice whether the rpms were up on the tach, as I was shifting. It seemed to happen as the rpms increased. I also noticed (okay, don't laugh at female description) a kind of fluttering in the accelerator pedal as I was pressing it down just before the lights went on.

Thoughts please? (Stick to car issues, haha).
Marci

There's a voltage regulator that used to be part of the alternator assembly, and may still be. It senses the alternator output and adjusts it to match the needs of the car under a wide variety of conditions. The output is normally more than 12v, so them saying it's higher is meaningless. The question is how much higher, and where it was measured.

Intermittant symptoms are difficult to diagnose with any degree of certainty, which is why anybody doing troubleshooting would like the symtoms to persist long enough for them to perform their tests. This doesn't mean they should scratch their heads and give you a blank look as to what might be the possible causes, because there aren't all that many, and they don't take all that long to check.

Hi Anonymous,
Thanks for responding. I was perusing the various other message threads and wondered if it was possible that the mechanic left the engine running while doing something that involved disconnecting the battery? I picked up the fact that this is a no-no with modern cars with computers. Also, do you know if there is any diagnostic indicator that would indicate that this was done, thus screwing up the alternator?

I am also trying to understand how all this just seemingly coincidentally happened AFTER I had the car check-up. Can you think of anything involved in changing the drive belts that could explain why this problem arose just after servicing rather than before? Or, could it really be the onboard computer?

My husband's uncle suggested our disconnecting the battery for a while and then reconnecting it. This would reboot the computer. We've done that and will be running a few errands and stopping by Salvo autoparts to look at Chilton to see how involved it would be for us to replace the alternator. If we can't do it ourselves, then we will take it to our local service station. Hope they have the appropriate diagnostic tools for Mazda. I don't know how different these things are from automaker to automaker.

The only reason I took it to the dealer shop is that I was used to taking it to them for some warranty issues which included three remote door locs, the CD player and the Mass Airflow Sensor, all of which needed replacement during warranty. The shop was very good about all of this and even replaced one door lock just after warranty went off. Also, it was their make of car and I thought they would know the most about it. I thought I trusted them, but now I'm not so sure. A neighbor's stepson had brake work done there and they put two different sized brakes on his car. Don't know if it was front or back brakes. So, you see why I don't want to take it there.

Thanks for any suggestions.

Marci

Disconnecting the battery while the engine is running is indeed a no-no on modern cars. This is because the alternator output is basically sensed at the battery and not at the alternator output terminals (This is desirable for several reasons).

Disconnecting the battery causes the regulator's point of reference to fall to zero (rather than being the nominal battery voltage).

The regulator isn't designed to recognize that the battery's been disconnected because this is an unnatural condition. So it tells the alternator that the battery isn't receiving a charge and to deliver more output. This can snowball out of control and cause the car to suffer the electrical equivalent of a heart attack. And you know what heart attacks can do.

Loss of alternator output isn't a problem when it comes to potentially harming things, but loss of the battery can cause all sorts of grief.

Alternators, computers, light bulbs, stereos, and a bunch of other stuff can potentially bite the dust if someone disconnects the battery while the engine's running -- especially if they're foolish enough to start turning things on.

There are typically various safeguards built in (like fuses, as a for instance) to protect against catastrophes, but they can't handle all the possible scenarios.

On most cars, the dash warning light will alert the driver that something's amiss, although not what, but most don't notice it until after the fact, and fewer still recognize the significance.

The mechanics should check to make sure that the alternator's properly grounded and that the associated wiring and its connections are themselves are in good electrical condition. The battery cables should also be checked to insure that they make good electrical connection to their terminals, and the terminals to the battery posts.

The charging system is not associated with the onboard vehicle computer except in an incidental way, so I wouldn't be inclined to blame it for any battery/alternator problems. But those kinds of problems, depending on their nature, can indeed have an adverse effect on the computer.

Disconnecting the battery for several minutes will reset the computer. But if it's the adaptive type that recognizes your driving style, it'll have to re-learn this.

The stereo will likely have to be reprogrammed and the clock reset.

Oh, there's also a remote possibility that you got a bum replacement alternator or battery.

Take a deep breath and let the guys locate the trouble. They will if they approach things in a logical, methodical fashion. But threaten to call in the Mafia if they try to charge you an arm and a leg for what is is basically a straightforward job.

And don't forget to make sure that everything works normally before you leave the shop.

I GOT THE SAME PROBLEM .. DOES ANY ONE KNOW THE CAUSE ? MARCI PLEASE GET BACK IF YOU FOUND ANYTHING OUT