Bad voltage regulator?

What did the people actually see? It is possible that they are using testing equipment that is different. Different testing equipment might have different cut-offs for good, bad and marginal. In addition, they may have interpretted the results differently.

I always like to get the real test results, not just good or bad.

Jeff

Yes, it is possible that both shops were truthful and the problem is intermittent, and it is possible that someone is just trying to make a sale or made an incorrect diagnosis.

What year and model vehicle? How many miles? How old is the battery?

You will more than likely have to replace the alternator. Repair parts for the internals used to be available such as voltage regulators, diode bridges, brushes, individual diodes, ect. Unfortunately that is usually no longer the case. An intermittent problem can be caused sometimes by an internal component failure due to heat build up during normal operation; such as when the vehicle starts up cold and the no charge light is off, then fifteen minutes later is starts blinking or fully illuminates. Is the no charge light illuminated at all? If it is on and then goes out after rpm is increased then the problem is usually the brush set. If you have a voltage meter you can test the alternator voltage output yourself at the battery, ( approximately 13.5 to 14.7 volts DC). If voltage decreases as the alternator warms up, the cause is usually a voltage regulator, or a diode, or diodes. If you are reading only battery voltage (essentially no alternator output) as when the car is not running, then windings, slip rings can be suspect. Voltage meters are relatively inexpensive now days to purchase. Good luck.

It could be the voltage regulator, electronics sometimes go intermittent but they won't stay that way for long. I'd think it is probably the brushes if you have more than 50k miles on the car. They wear down and will sometimes get kicked back up into their track and will lodge cocked a little. Then a jar from a bump will nock them loose and the alternator will work again.

Either can be replaced without buying a new alternator, if you can get the parts. It would be best to replace the alternator if the problem is either the brushes or the regulator. Those parts can only be replaced by disassembling the alternator. You stand a good chance of loosing the little pin bearings at the rear of the alternator, not to mention getting dirt in them.

BTW, battery voltage should be around 14 to 14.5 volts with the engine idling and all accessories and lights turned off. It will drop a few tenths as the alternator gets warm.

Good luck Jack

Unfortunately, RI, you don't say what year or model.

In my '85 Celica, the radio blew a fuse. Huh? Why'd it do that?! Then I looked at the voltage guage...pegged. A VOM said 19 volts. Now, I was working at a CarQuest store, so I bought a regulator and a set of brushes for $53 (employee discount...the regulator alone was $53 list.)

Took the alternator out, and yanked the VR...the new one was the SAME, same part number, same manufacturer. Replaced the VR and the brushes; they were about 1/2 worn but since I was in there.

Ran great for three more years, then I gave the car away.

It's a 95 Geo Prizm and it's about to turn 160K miles old. I don't know the age of the current battery because it's the battery that was in the car when I bought it. Both O'reillys used a tool to test my car that looked exactly the same. As of yet, I've seen no warning lights lighting up on the dash.

I'd bet that a door was not closed all the way, draining the battery or the problem is intermittent.

Then I'm guessing it's an intermittent problem because making sure that all the doors are closed is one thing I am sure to always do ever since one of the doors became a little harder to get latched. Nowadays you have to shut it just a little harder. I also usually keep the dome light switched to the off position because of this.

11 years is just about right for the brushes to go bye-bye. Do you think you can handle a 'rebuild'? I would get brushes, a regulator, and bearings. Big mistake I made with my Hachiroku was not replacing the bearings when I had it off in 92. Now, the bearings are shot and I CAN'T get it off the car!!! Use anti-seize when reinstalling, just in case!

I would not go with an aftermarket rebuilt. The good ones have about a 40% failure rate, and the cheap ones run about 65%! There was one brand, I can't remember; the manager at CarQuest told Corporate not to even bother sending them anymore.