How To: Test if Your Alternator is Bad - The Easy Way.

How To: Test if Your Alternator is Bad - The Easy Way.

You know the scenario.  Your car is hard to start, or you've come to rely on jumper cables.  How do you know if it is your battery going dead, or if your alternator is bad?

Theory: Most vehicles do not operate on the battery.  Instead, it is the alternator that supplies the electricity when the vehicle is running..  The alternator also "tops up" the battery when it is discharged.  This article assumes you know how to tell the negative and positive battery terminals apart.

Step-by-step instructions:

1. Have your tool kit handy, you will likely need to loosen a bolt.

2. As this test may STOP your vehicle, be near some way to start (boost) it again.

3. Start your engine and let it idle.

4. Find the POSITIVE battery post. It is usually the one with a red cable connected, and is usually slightly larger than the other battery post.  Either way, be certain before you proceed.

5. Loosen the clamp and remove ONLY the POSITIVE battery cable.

6. If the vehicle stops instantly, the problem is probably your alternator, not your battery.

OTHER INFORMATION:

This is a diagnostic test only.  There could be a variety of other problems, such as loose wiring, wet wiring, or a short circuit.  The test here is to eliminate your battery as the probable cause of hard starting, thus potentially saving you the time and money of a needless replacement.

Be careful when boosting computer-equipped cars, it is possible to damage the computer if the driver of the vehicle being boosted revs his engine when it starts.  Be ready to remove the cables instantly after the boosted engine starts.

Helpful hint: if you have two sets of cables, you can hook them both up and effectively double the amount of "juice" flowing to the dead battery.

Another helpful hint: if the battery is completely dead, it may not be able to charge enough in a reasonable time to start the stalled vehicle.  Try removing the POSITIVE battery terminal and connecting it directly to the correct jumper clip.  Replace it when the vehicle is running.

Source: Tales From The Trailer Court™ .

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Disclaimer: veryatlantic™ is a non-technical source for advice and entertainment and is not responsible for any damages under any theory. All posts sacrifice technical accuracy for user-friendliness. If unsure, get help. Please feedback errors for correction.

This article written May 29, 2010.

This article updated June 22, 2010.

Comments (1)

iTony said:

	... This is one of the quickest ways to test your alternator.
	report abuse vote down vote up

March 27, 2010
Votes: +0