Alternators serve two distinct purposes on any vehicle, the first is to provide power to meet all of the electrical needs while the engine is running (electrical system, lights, interior accessories, etc). The second is to charge the battery, so it will have enough power to prime the fuel pump, crank the engine and start the vehicle.
There are many things that go wrong with the electrical systems on a vehicle, and typically it will boil down to something other than a major component. Corrosion, grounding issues, and open circuits are the three main culprits when you are trying to find a problem. So, rather than “throwing parts at it,” first you will need to try and pinpoint what is actually wrong.
Q: I took the readings and the voltage is less than 0.5V above battery voltage. What does this mean and what do I do?
(Tool Q&A Question 3: Verify the voltage the alternator is producing)
A: Normally this is where you would replace the alternator. However, there are a couple other factors that you need to take into consideration and think about prior to buying parts.
- Does the vehicle have aftermarket addons? I.e Stereo, subwoofer, sound system, alarm, additional exterior lighting, etc. These things can add a large power draw onto a vehicles stock electrical system, and can cause many issues. If they require more power than a stock alternator can produce, then swapping it out with an OEM replacement will not solve the issues. You will need to have the customer remove the aftermarket accessories OR you will need to install an alternator with a higher AMP rating than the one you are removing.
- Some people have heard that rebuilt alternators and new alternators are not the same quality. They think that buying an OEM one ensures they are getting a “good one." The problem is that all companies occasionally have manufacturer defects with products. You should always have the “new” or “rebuilt” alternator bench tested at your local autoparts store prior to installing. This will ensure it is producing the correct voltage, and that the diodes & voltage regulator inside the unit are functioning correctly.
- Some vehicles have external voltage regulators. This controls the voltage that the alternator produces. So even if the alternator is not producing the correct amount of power, it may be the external voltage regulator causing the issue. Many alternators however, have an internal voltage regulator, so you need to swap out the whole thing to fix the issue.
- Lastly, some vehicles have issues with the ECU failing, which can cause the voltage regulator to fail/work incorrectly. If that is failing, it may require an ECU swap to resolve your issue.
