The alternator is among the easiest automotive parts to replace, which is convenient because almost everyone has had to.
Years ago, when the alternator replaced the venerable generator, talk in the aftermarket was that there would be no need to replace them, that they would last forever. Well, we’ve heard that before, and since, but alternators often undeservingly bear the brunt of repeated failures. Here are seven reasons alternators may end up back on your counter.
SIN #1) While certainly not the most common or popular reason, sometimes a replacement alternator is actually defective. It’s not usually the case, but let’s be honest, mistakes do happen. They just don’t often happen more than once on the same vehicle.
SIN #2) The alternator was used to charge up a rundown battery. Usually the second or third alternator will last, since the battery is fully charged by then.
SIN #3) The alternator tried to charge a dead battery that should have been replaced. No amount of alternators will solve this one.
SIN #4) The alternator installed was of a lower rating than specified (e.g. a non-a/c amperage when the car was equipped with a/c), or the load on it has been greatly increased by adding lots of accessory lights, communication equipment, or an ear-splitting sound system. Overtaxed, the alternator tries to keep up and burns itself out.
SIN #5) Blaming the alternator or component when it’s actually fine. Example: On GM CS alternators with a Powertrain Control Module (PCM) activated regulator, the regulator is activated by a voltage sent to the “L” terminal, which can be below 1 volt. Since a 1-volt threshold is often used to determine good from bad when tested, it might be incorrectly rejected. However, these regulators may work fine on the vehicle when they ramp up to a more acceptable 5 volts or so.
Also, the CS130D has an internal temperature sensor that shuts the unit down when its temperature exceeds 280 degrees F. If a unit is tested when it is this hot due to idling in traffic–even in winter, if snow is blocking the grille for example–it will stop charging and the dash warning light will illuminate. Once it cools off, it will resume normal operation.
On many Honda models, alternators don’t provide full charging output for a full minute after startup. Checking output too early will cause a technician to draw the conclusion that the unit is bad, when he just needed to wait a minute before testing it.
SIN #6) Alternator was not the problem to begin with. Usually the real reason is old or poor connections or just poor diagnostics (“Didn’t start before, replaced the alternator, still doesn’t start.”) and you end up looking at the same unit again.
A good example is that some Ford models have a fused connection to the “A” wire feed on the alternator. This can blow when the coil shorts or when the brushes become so worn that they short out. So, even if the alternator that the tech takes off is actually bad, none of the subsequent ones will work at all if he’s not aware of the blown fuse.
SIN #7) Belt tension way too tight. This will burn out a bearing in a very short amount of time.
There are more creative ways to kill a good alternator than you can imagine. The best way to deliver yourself and your customers from unnecessary failures and comebacks is through training and encouraging effective diagnostic procedures.
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