2001 Cavalier Battery Drain Problem - HELP

[J-Ri]

You shouldn't have any AC voltage across the battery terminals. It's acceptable to have a few millivolts AC leakage out of the alternator, but should never be even close to what yours is. Your alternator is junk, the rectifier is bad allowing AC voltage out. The alternator produces AC current which is then converted to DC inside the alternator. Check out http://en.wikipedia.org/wiki/Bridge_rectifier for a full explanation of that. Don't run the engine any more until you replace the alternator, as it could damage the new battery. Basically, the alternator is charging and discharging the battery thousands of times per minute, and at a much higher voltage (almost 3x) than the battery is designed for.

[manicmechanix]

Yeah I definitely agree there should be only a few millivolts of AC votage at the alternator +B. I think I gave incorrect info about there being any AC voltage above a few millivolts across the battery. There shouldn't be across the battery either. There's little clear info out there about AC voltage in the charging system and some sources claiming as long as it's under 30V that's normal and I think that's wrong. Electrical is still my weak point. I agree with J-ri.

Your alternator is probably bad due to faulty diode(s) in the rectifier (very common problem) and is why you were having battery propblems. That's why I suggested you have it load tested and asked if you had somewhere between 13.6 and 14.8V with the new battery (even then it could still drop under load). You should have the alternator tested on or off the car and replace it.

[amberdamber7]

Allright, another update... so I replaced the battery, and the drain continues (although not quite as fast, still loses .5-.6 volts in 3-4 hours). So, it wasn't the battery after all. Amp draw remains .08 amps when the car is off (I checked across the console fuse, and ALL of the amperage is running through there).

Today, I took the alternator (thinking it might be a diode) to Autozone. They put it in their machine, and it passed with flying colors. While removing the alt, I checked amperage in line with the positive connection, and it was 0. So, it wasn't the alternator diodes.

Here's the weird thing: After reinstalling the alternator, I fired up the car for about 10 seconds and shut it off again. I went to check the belt, and heard a very faint high-pitched whine coming from the alternator - I've never heard this before, but I never got that close to the alternator before either (almost touching it with my ear). Confused, I checked the voltage at the battery and it had lost .3 volts in just a few minutes (could have been from starting the car). I checked voltage between the battery positive and the alternator positive - .01 volts. I checked amperage, and came up with .01 amps. This whole time, the whine was still there. Finally, I disconnected the battery and the whine stopped - the voltage and amperage between the battery positive and the alt positive had stopped as well.

I reconnected the battery, and there was still no whine. Checked the battery voltage, and it had gone back up .2 volts. I restarted the car, ran it for a few minutes, and shut it back off. The whine was back again! This time, instead of disconnecting the battery, I disconnected the plug on top of the alternator (I think the sensor?) and the whine stopped again. I reconnected the plug, and no whine. I restarted the car, ran it again for a few minutes (turned a few accessories on and off, checked the charging voltage of the alternator (14.5), then shut the car off. This time, the whine did NOT come back. Nor did the volt and amperage running from the battery to the alternator.

So what the heck is going on here? Besides this new thing (the noise the alternator is making), the only other thing I think of is that the computer is turning something on every few hours, and I have no way of testing that. Nor can I test the actual drain on the battery when the alternator is making that noise, because disconnecting the battery to test is stops the noise! Aaaaaarg. Thanks for listening everyone!

[J-Ri]

The battery voltage dropping .5-.6V in several hours may be normal. What's the voltage at after it drops?

If you had 30-some volts of AC voltage across the battery terminals, the alternator is bad. It should not allow more than a few millivolts of AC voltage. Double check that your meter wasn't on auto-range and reading mV.

The whine from the alternator is not normal, and also suggests a bad alternator.

The connector you disconnected from the alternator is the "no charge" indicator and the "GEN-L" wire. The no charge wire provides a ground to the no charge indicator light when the alternator is not charging. The GEN-L terminal is an input to the alternator that controls the duty cycle (% on-time) of the field coil. That is how the output from the alternator is controlled. Remove this connector and check the amperage on that fuse again. On some models, the alternator is controlled by the instrument panel module.

If you want the check the parasitic draw without disconnecting the battery, get a clamp-on inductive ammeter. I've got one that was a couple hundred $, but sears has one that looks good for around $70. They're not quite as accurate as the probe kind, but are much more convenient and work just fine for finding parasitic draw. I still don't think you're draw is too high. .05A is good. Like I said before, .08A for 100 hours is only 8 amp-hours, which is nothing on a 60 amp-hour battery. It's leaving you with approximately an 87% charged battery after it sits for 4 days.

EDIT: I went to the Exide web site to see if I could find the amp-hour rating for a 75 series battery. I couldn't, but the reserve capacity@25 amps is 90 minutes, which is 37.5 amp-hours. And that's to where it will still pass a load test. http://www.exide.com/products/automo..._60_specs.html That's their lowest quality battery, and Exides are certainly not the best brand, so chances are you got a better one (Guessing Duralast since you had it tested at AutoZone)

[amberdamber7]

As an example of the voltage drop in 4 hours, on Friday the battery voltage went from 12.7 to 12.25 in just over 4 hours. It still started just fine at that point, which is definitely more than the old battery could pull off!

The instruction manual for my multimeter doesn't mention autoranging, so to test that idea I checked AC volts on my other car (2005 Matrix) and got the exact same reading (30-32). That car has no problems with battery holding charge, so you are probably right about the auto ranging (or I am doing something wrong with that measurement).

I turned the ignition in the cavalier to "on" without starting it, and the alternator makes that same noise in that situation, and shows voltage from both wires going into the alternator harness. When I took the key out, the noise stopped. Besides those first two times, I can't make it happen anymore (maybe I had the plug a little loose). So now I am letting the car sit overnight again to see if there is still a draw, or if I somehow magically "fixed" it by monkeying around with the alternator.

[J-Ri]

Originally Posted by amberdamber7

The instruction manual for my multimeter doesn't mention autoranging, so to test that idea I checked AC volts on my other car (2005 Matrix) and got the exact same reading (30-32). That car has no problems with battery holding charge, so you are probably right about the auto ranging (or I am doing something wrong with that measurement)

Well, to begin with, a computer controlled car should not run at all with that much AC voltage because it would screw up the computers inputs and outputs so badly. So, I bet it's something in the meter, mine never reads over a few mV on a good alternator.

There's also a possibility your meter is wrong. What brand is it? If we're talking about fixing an error of .03A, I would ignore it unless you're using a Fluke or another high quality meter. Also, you can check the accuracy of the voltage by checking a new AA battery. Should be very close to 1.6V out of the box

[manicmechanix]

Originally Posted by amberdamber7

Allright, another update... so I replaced the battery, and the drain continues (although not quite as fast, still loses .5-.6 volts in 3-4 hours). So, it wasn't the battery after all. Amp draw remains .08 amps when the car is off (I checked across the console fuse, and ALL of the amperage is running through there).

It might not have been the old battery causing the drain before but the battery was probably ruined. If you are losing .5-.6 V then your battery is discharging. You are not showing a parasitic drain so you add that to the AC voltage you found and the alternator whine and it all adds up to a bad alternator.

Today, I took the alternator (thinking it might be a diode) to Autozone. They put it in their machine, and it passed with flying colors. While removing the alt, I checked amperage in line with the positive connection, and it was 0. So, it wasn't the alternator diodes.

The thing is if all they do is test the voltage output it may not show the problem. The amperage has to be checked under load. there is a possibility they didn't check your alternator right. There's also a possibility you have a problem in the circuit at the PCM connecter at the alternator, but very doubtful if no check engine codes for are being set.

Here's the weird thing: After reinstalling the alternator, I fired up the car for about 10 seconds and shut it off again. I went to check the belt, and heard a very faint high-pitched whine coming from the alternator - I've never heard this before, but I never got that close to the alternator before either (almost touching it with my ear). Confused, I checked the voltage at the battery and it had lost .3 volts in just a few minutes (could have been from starting the car). I checked voltage between the battery positive and the alternator positive - .01 volts. I checked amperage, and came up with .01 amps. This whole time, the whine was still there. Finally, I disconnected the battery and the whine stopped - the voltage and amperage between the battery positive and the alt positive had stopped as well.

OK there's bearing whine (more like sqeak) and there's alternator whine which usually indicates bad diodes. Sounds like diodes. If you measure across the BATT terminal with it hooked up like that, you're not going to see any volts or current. You need to put the multimeter's pos terminal on the alternator BATT and the meter's negative terminal to ground.Also it's not a good idea to unhook the battery with the key on ON or engine running.

I reconnected the battery, and there was still no whine. Checked the battery voltage, and it had gone back up .2 volts. I restarted the car, ran it for a few minutes, and shut it back off. The whine was back again! This time, instead of disconnecting the battery, I disconnected the plug on top of the alternator (I think the sensor?) and the whine stopped again. I reconnected the plug, and no whine. I restarted the car, ran it again for a few minutes (turned a few accessories on and off, checked the charging voltage of the alternator (14.5), then shut the car off. This time, the whine did NOT come back. Nor did the volt and amperage running from the battery to the alternator.

It's not a good idea to unhook the connecter at the alternator with key ON or engine running either. When you got 14.5 V at the battery that indicates your alternator was charging the battery at that time. You might have an intermintent problem.

So what the heck is going on here? Besides this new thing (the noise the alternator is making), the only other thing I think of is that the computer is turning something on every few hours, and I have no way of testing that. Nor can I test the actual drain on the battery when the alternator is making that noise, because disconnecting the battery to test is stops the noise! Aaaaaarg. Thanks for listening everyone!

You don't really need to unhook the Battery. Just measure voltage across the battery terminals and see if it's in the 14V range. You can also check that you have +battery voltage between the Alternator + output and -battery terminal with key ON. You can inspect the connections and wires at from the alternator.

I think you should take it to a different autozone or advance and see if they can test your alternator on the car properly. I still think you have a bad alternator.

[J-Ri]

Originally Posted by manicmechanix

It's not a good idea to unhook the connecter at the alternator with key ON or engine running either.

Reread what he originally typed, I take it to mean that it was making the noise with the engine off, which would certainly indicate a problem with the electrical part of the alternator. OP, can you clarify whether the noise was with the engine running or with the engine off?

[amberdamber7]

Sorry if I was unclear about that noise - it was definitely present with the engine OFF; don't worry, I would never disconnect anything with the car running (its broke enough as it is!). To make it a little more clear, it is a very high-pitched whine, but it is EXTREMELY quiet. I had to have my ear about 3 inches from the alternator to hear it.

The noise comes on when I turn the ignition key to "on" without actually starting the car. Occasionally, it stops when I take the key out, but it sometimes does not stop until I disconnect the battery or disconnect the wiring harness on the alternator. My guess at this point is that it is a noise related to the field generator - unfortunately, I think this means the PCM is leaving the field generator on when the car is turned off (sometimes). Like I said before, I don't have a way of testing this because, convienently, disconnecting the battery or removing the fuse stops the problem - then the draw reverts back to .08 amps (of course, this is just a theory at this point).

Finally, I noticed the other day, and again today, that the black plastic part of the alternator (it has little vents on it, and is where the harness plugs in) wafts warm air when the engine is cold. The alternator itself is NOT warm to the touch - and I wouldn't say the black plastic part is "warm," its more like a slightly warm draft rises up out of it. At autozone, they told me that this is normal if there is a big drain somewhere else in the system, as all the power from the battery runs through the alternator on its way to the rest of the car. I don't really agree with that, and I think this is an important clue to the problem.

Let me know if this clears up my current situation!

[manicmechanix]

I was just cautioning not to unplug the battery and the alternator connector with key ON or in RUN, not saying you have that's all. I would forget about the PCM connectors to the alternator. You don't have any trouble codes related to this circuit, and the way to test it is with a scanner and backprobing the connector with a voltmeter, and the battery doesn't need to be unhooked anyway. I doubt your problem is there. The field and rectifier are always "on" because it's hot at all times from the battery. You have some noise in the alternator with key off. Why not just simplifying things and have the alternator properly load tested on the car at one of the parts store. I'd be surprised if it passed, unless it was an intermitent problem.

[amberdamber7]

This is probably the final post until this problem starts happening again (if?). Since I installed the new battery, the car has not been dead in the morning - although I unplugged the battery at night for the first few days. The voltage is always lower in the morning by .3 or .4 volts, so if the drain is still happening the battery is taking it well. I will let it sit this weekend without driving it to see if the drain will take the battery out after 24-36 hours (it hasn't sat for any longer than 12 in the past week). If it does, it will be going to the shop as I have simply run out of ideas (not to mention patience). If that happens, I will post the results! Thanks to everyone for helping me out, you've probably saved me a lot of money!