How to tell if it's the alternator or battery..?

[Don in Austin]

Originally Posted by Caligula1

Seems a very long time ago I remember someone showing me to remove one of the Battery cables while the car was running to test if the Alternator is indeed dead or the Battery..

Was I dreaming or this just a figment of my imagination..?

I need to try a home test of some sorts to figure it out..

This test is ignorant. First off, it is not at all accurate. Indeed, it can verify that the alternator puts out SOMETHING, but can not verify output is correct.

Much worse, it can allow voltage spikes that can damage expensive electronic modules.

You can do better with a $5.95 multimeter from Harbor Freight.

Don in Austin

[Don in Austin]

Originally Posted by cab591

Rare for a 1 year old battery to die, but I've seen it before. I'd put my money on alternator though. If the battery isn't charging enough when the car is running, it'll continue to die. Like I said in my post last year, take it to an auto parts store (O'Reillys, Autozone, Napa, Canadian Tire for our northern friends...). They'll check it for free.

Side note, because Pep Boys has an actual shop (with real mechanics,

"Real mechanics" at a Pep Boys? That is a matter of opinion -- I disagree.

Don in Austin

Originally Posted by cab591

and shop insurance), they'll charge for things like battery changes (but I think they'll still check it for free). O'Reilly's and AutoZone will swap the battery for you for free (though the employees do appreciate small tips!).

[Ccm704]

I have a 2003 ford taurus ses and the air compressor locked up and it thru the belt. Then the battery light came on and I assummed because the alternator was on that belt circuit. We did replace the compressor but the battery light hasnt gone off. I assumed once belt and compressor replaced it would go off. Any advice?

[wankel7]

Originally Posted by Ccm704

I have a 2003 ford taurus ses and the air compressor locked up and it thru the belt. Then the battery light came on and I assummed because the alternator was on that belt circuit. We did replace the compressor but the battery light hasnt gone off. I assumed once belt and compressor replaced it would go off. Any advice?

When the belt flew off it could have damaged the wires that go to the alternator. Check that out.

[pineivy0911]

2001 dodge dakota quit while driving lights come on and the starter clicks but won't start

[brandonbelcher]

1999 c280 power steering went out then battery light came on. The next day the car died driving down the road. Must be the alternator ?

[SchreddarPwnz]

If you are stuck on the side of the road without a voltmeter and trying to troubleshoot, start the car, remove the negative battery cable, with my Jeep serging the positive side is bad for the electronic relays and computer, always negative First or only, you only need to remove one terminal to determine if the car is able to continue running at idle under the alternator power, do not rev the motor or attempt to change the idle speed of the motor if the battery is in any way disconnected intentionally, when the car goes from high to low idle you may notice stuttering, this is when the motor usually feeds off the battery as the engine RPMs drop to compensate for the voltage needed to maintain steady RPM. Doing this for a few moments is all it takes to determine if your alternator is capable of keeping the car running, I'm not a Certified mechanic so I can't guarantee this works on all vehicles, but it has worked for me without issue thus far. If you notice while driving the car tries to die when coming to a stop, typically this is because the battery does not have enough charge to maintain the RPM steady as RPM decreases while coming to a stop, and I know this because I had to jump my car with a spare battery at three stop lights haha, the fluid level should be to the bottom of the fill holes in your battery and no lower than that while it's on a level surface, if the battery is topped off and you're still having issues you may need to replace the battery if you've already tried checking the acid chemical levels of the battery with the proper tools, the little dropper gauge is around $5 and a battery acid refill kit is around $15. I wouldn't tamper with batteries on a hybrid if you don't know what you're doing, you can weld yourself to it with the amount of voltage under that rear seat.

[tickyul]

A good battery, that has been fully-charged and serviced, should not fall below 10-volts when starting your vehicle.

You can attach a voltmeter on to the cigarette-lighter and start your vehicle, use the low-hold feature if you have it.