Volt gauge dropping to 9

Jeepguy91 · Mar 19, 2013

We are having a problem with the volt gauge in our 2000 xj dropping to 9 and the check gauges light coming on when we are driving it. You can start it up and it run just fine and then all of a sudden it goes and drops to 9 and the light comes on. I have gone thru and cleaned up all of the ground locations and have had the alternator and battery checked and everything checked out good. The way that i have been fixing this is by taking the terminals off and cleaning them really good again and putting everything back together and it it good for a week or so then it happens again. Im starting to think it has something to do with the battery but am not sure and don't want to drop the money on a battery if its not what the problem is. Do you guys think i should go ahead and buy a new battery for it? As of right now that is the way that i am leaning towards cause i have tried everything else.

Thanks,
Ben

sidewaysstarion · Mar 19, 2013

It sounds to me like a failing alternator.

Jeepguy91 · Mar 19, 2013

Alternator has tested good both times i've had it tested

Sidewinder CC · Mar 19, 2013

Jeepguy91 said:
We are having a problem with the volt gauge in our 2000 xj dropping to 9 and the check gauges light coming on when we are driving it. You can start it up and it run just fine and then all of a sudden it goes and drops to 9 and the light comes on. I have gone thru and cleaned up all of the ground locations and have had the alternator and battery checked and everything checked out good. The way that i have been fixing this is by taking the terminals off and cleaning them really good again and putting everything back together and it it good for a week or so then it happens again. Im starting to think it has something to do with the battery but am not sure and don't want to drop the money on a battery if its not what the problem is. Do you guys think i should go ahead and buy a new battery for it? As of right now that is the way that i am leaning towards cause i have tried everything else.

Thanks,
Ben

Have the battery capacity checked at a trusted shop. Use two different shops to check it if neccessary. If it is a wet cell battery, i.e., one that you can remove the top covers and look inside the battery, check the electrolyte level and see if the fluid is below the plates. You can top it off with distilled water to just above the plates.

If the battery is over five years old consider a new battery. Group 34/700 cranking amps.

Jeepguy91 · Mar 19, 2013

I've checked the fluid in the battery and it is topped off. Think the battery is around 3 years old but it is a smaller battery. Im thinking only like 500cca or somewhere around that. I did use the battery to run a winch once. Could that have killed it to make it start having these problems? it just seems like it loses connection with the terminals and then the gauge drops. I've also been putting anti corrosion spray on the terminals and doesn't seem to help.

dsdtdemon · Mar 19, 2013

Does the gauge show 12V when the engine is not running? If so, the problem is likely in the alternator system somewhere.

Tim_MN · Mar 19, 2013

Alternators with failing brushes commonly test good on the bench, and intermittently fail under driving conditions.

WB9YZU · Mar 20, 2013

The OBDII Models indicate a low voltage, then drop it to zero and light the check engine light to remind the driver that something is amiss.

Everytime it has happened to me, it has been the alternator.

A few things to test if you want:

3 wires to alternator. 2 for field, one for output. If you have field input, but no alternator action, the alternator is bad.

The field is fed from the PCM.

Also check a couple of joints. The positive battery cable connections, both sides. Make with the battery disconnected, you can verify with a ohm meter or continuity tester that the cable is making connection at the alt and positive.

Make sure ground straps from engine to battery are making contact with a continuity tester.

Talyn · Mar 21, 2013

I gave up on taking the alternators to Advance, Autozone, etc to have tested. They are seldom right.

x2 on the alt being bad.

Volt gauge dropping to 9

Jeepguy91

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sidewaysstarion

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Jeepguy91

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Sidewinder CC

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Jeepguy91

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dsdtdemon

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Tim_MN

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WB9YZU

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Talyn

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