How to test for bad alternator. Internal shorts etc

Solution to a very hard to diagnose issue on a 99 Honda Civic. The issue can be found on any car and here is the solution.

Here are the facts to help you diagnose if the below is the same for you:

Battery - good and tested by autoparts store

Alternator - good and tested by autoparts store (outputs 14v when car is running)

When testing amperage from + battery post to + battery cable, NO current draw is found.

The mystery here is why the battery is draining. Since no relay/circuit is showing a draw, the draw is occuring from wiring not included in the large harness that powers all of the components inside your car, and in the engine bay. The only cable that hooks up avoiding this is the cable that the alternator uses to charge the battery.

With car engine off,
Test the battery's voltage after charging and disconnecting the cable coming from the alternator. You should have over 12v.

Keep the meter on the battery, and then reconnect the cable from the alternator. If the voltage drops, and keeps dropping over a period of minutes, you have a bad alternator. Even though it may charge, it has an internal short and needs to be REPLACED.

I hope this helps everyone figure out this mystery issue that can occur from time to time.

Category:

Autos & Vehicles

Tags:

• Honda
• Civic
• Alternator
• Japanese
• Test
• Electrical
• Charging

[gasper44]

@kevinermitchell

Look at voltage regulator. In hondas, they are generally on the alternator itself. In other makes, sometimes they are mounted in the engine bay/connected to ECU.

[kevinermitchell]

coz dash lights flicker bad how i fix that?

[gasper44]

Also wanted to add that you never want to test voltage on your multimeter when on the amperage setting (you will blow the fuse!). I learned this lesson a long time ago in electronics courses when I was younger.