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Battery, Alternator, PCM, or What?

(2002 Mazda Tribute)
in Omaha, NE on June 11, 2011
Approximately 3 years ago, I replaced the alternator on my wife's 2002 Mazda Tribute LX (3.0, 6-cyl, 4WD). Sometime after that (a few months), she informed me that at random intervals, all of her gauges (speed, fuel, etc.) would peg out at the top end of the scale, then return to normal. I attributed this to a possible faulty ground, but never did find the problem and it didn't seem to affect her everyday driving, which is somewhere around 500 miles/month.

On her way home from work last week, she called to let me know that her battery light and brake light had come on, her gauges had pegged a couple of times, and that her windows wouldn't work. I told her to shut off all accessories and come directly home, since it was likely she was only operating on battery. She made it home, where I found that the battery was dead. Hoping to avoid the chore of changing the alternator again, I had the battery tested and it had a dead cell. I installed a new battery and she took the car to work the next day. On her way home that evening, her battery light came on again. The next morning, I put a meter on it with the engine running, and found that the alternator wasn't charging. I purchased and installed a lifetime-warranty re-manufactured alternator from NAPA, which tested good at the store.

The following day, I took the care for a 15 minute test drive and had no problems. However, the next time my wife took the car to work, her battery light and brake light came on while driving, and the gauges pegged out several times, again.

The car has a new battery which tests out okay, and a "new" alternator, which also tests out okay (charging above 13v under load). I also ran new ground straps from the negative terminal of the battery to the firewall, and from a stud on the engine to the frame, just to make sure that a loose ground wire wasn't causing the problems. The battery light continues to come on intermittently, and the gauges peg out randomly, as well. I'm stumped, unless it's a "computer" problem (Powertrain Control Module?).

Any help would be greatly appreciated! Changing the alternator on this little SUV is a real pain, and I'm not convinced that doing so (again) is going to solve the problem.
Displaying 1 answers & 3 comments
Popular Answer
on June 12, 2011
Your alternator needs to be charging at or above 14 volts at 2000 RPM. I suspect a faulty alternator again.

Verify also your wiring connector at the alternator - make sure the terminals are not damaged or melted.

Your powertrain control module is not going to be the failure.

Lastly - something else to consider is the ignition coils. If the coils are leaking some spark, even without a huge performance issue, there could be RF interference under the hood causing problems with the processor and charging system. I would recommend having a coil stress test performed with a high quality diagnostic tool. I have seen this before.
on June 12, 2011
Hi, Dave.

Thanks for the guidance and advice. It should help narrow the search for the culprit.

By the way: now that you've jogged my memory, I replaced two of the ignition coils last year, after getting a check-engine light and rough starting in damp weather. My son is a past mechanic, and was able to use his scanner to identify the weak coils.

My wife has mentioned that the car is once again starting with some difficulty, particularly in damp weather. I've been thinking that I should go ahead and replace the rest of the coils, but I never considered that they might be causing these other symptoms.

Thanks for shedding some light on the possible connection.

on June 12, 2011
Coils may be needed, at the very least coil boots should be replaced. The coil stress test is a good idea.
on September 26, 2011
I have the same car( 2002 tribute 6 cyl), same problem. charges at 10 volts idle, 14.5 at 900 rpm. battery gets dead overnight, sometimes while driving ! ****HOW do you get the Alternator OUT of this car ??!!*** can't come out the bottom, top or side . HOW is it done ?? Thanks for any help you can give.
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