Have a 200 mc ss, have been having this problem for the last 5-6 months. have been troubleshooting the issue, and still can not find out the problem. the car would die over night. just today took it to a place the specializes in auto electrical problems. They could not find the issue either said that is is something with the audio system. I have unplugged the factory radio and amp and the car would still die overnight. Any suggestings? Please!!!

 

My suggestion would be to have your battery load tested to see how well it holds up.To me it sounds like your battery isnt holding a charge and dies over night.It maybe that you need a new battery if the one you have is old? I recommend the Sears Die Hard Gold over any other brand...The optimas seem not to last too long for some reason...i had two of them and they only lasted me aprox 3 years. I really dont think that anything in your audio system in the car would be drawing that much power to kill your battery over night unless your amps are staying on? Load test your battery....you may need a new one?

 

Here's a link to a similar discussion:

https://montecarloforum.com/forum/ge...charged-25826/

Here's my input from that earlier thread:

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Ditto on the battery / alternator test. Take it to an auto parts store that will test both for free.

If battery/alternator test fine, you may have a current drain somewhere in the system. A quick fix to prevent the battery from dying overnight is to install a battery disconnect switch of some kind. Most auto parts stores would have one for ~ $20 - $40.

Finding a current drain can be a pain, but it's not impossible. You'll need a multimeter. Disconnect the negative battery cable; hook up one multimeter lead to the negative battery terminal, the other lead to the neg. battery cable (or to any other good grounding location you can find). Start with the multimeter on a high amp setting just in case there is a significant current drain; that way you won't fry the multimeter. Then change the multimeter setting progressively lower. Most cars will have somewhere around 15 milliamps running through the system to power radio clocks etc. So getting a small reading is OK. But if you find more than about that, you have something draining power.

To identify the circuit that's causing the drain, take out one fuse at a time, then look at the multimeter reading. If unchanged, replace that fuse and try another. Keep trying 'til you get a reduction in the current reading on the multimeter. Once you ID the circuit with the issue, you still need to figure out exactly what is causing the drain; but at least you'll then know where to start looking.
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Hope this helps.

 

Thanks for the reply,but i have had the battery tested and just put a new alternator in. I use to just be able to pull the battery/ amp fuse the the car would be ok over night. But lately that have not even been helping. So just today i bought a test light and disconnected the amp, radio, and the fuse and tested the connectors to the radio and the amp. I have a radio circuit diagram and the ports that are still active is the battery port and "computer data line system". the battery port is suppose to always be hot. but i do not know about the computer one. Do anyone know if that is suppose to stay active.

 

Plok....you didnt mention if you had the stock head unit or an aftermarket head unit in your Monte.If its a stock GM CD/Cassette head unit then both should be hot because the computer output is for the features to your car like the air pressure in your tires, oil change light, security system etc... The other port is most likely for your radio memory to hold your preset radio stations so that needs to be live in order for it to work...You also didnt mention how old your battery is? Why did you need to change out your alternator? Was your volt meter reading a low output or did you just replace it cuz of the dead battery issue? I still think you may have 1 or 2 dead cells in your battery and its testing fine for load when you take it to the shop for testing but it seems not to be holding a charge over night even though you unplug your head unit along with your amps...I still dont think its your stereo because you mention that your battery still dies over night even with the fuse pulled for the stereo and amps...Does your car start right up when someone jumps you after the battery dies? Battery voltage should be anywhere from 12.7 to 13.2 volts on a good battery when the engine is off...check it out with a voltmeter when your engine isnt running and several hours after not driving it and see what it reads.

 

Thank for the reply, sorry for the missed info. But yea it is the factory cd/tape HU. My battery is like 5 months old. And when i get it jumped it do start right up off of the first crank. Yesterday i did the solution about pulling the fuses and hooking the meter to the battery and the negative battery cord. I set the meter to 10A, the reading i was getting out 1.68amp when car was off. With the radio and amp unplugged i was getting around 0.69amps. So i started pulling fuses and when i pulled the fuse labeled CLSTR/BCM (Cluster , Body Control Module, Data Link Connector (Batter) TrapAlert System).The meter would drop down to 0.02 amps. Now i do not know if it did that because it is cutting all electric to the parts in the car or do i need a new BCM. By the way i changed the alternator because i went to several shops and told them my situation and the all would say it most likely is the alternator. I told them i had the alternator tested and it came back fine. But than they said that their is something in the alternator when i turn the car off, this thing would cut the electric current from the car and the battery, and that the alternator would test ok but if the thing was bad it can cause the battery to die.

Thanks for the help

 

You need to wait about 2-3 minutes after you close the last door before you start measuring current draw... that how long it takes for the BCM to go to sleep

Once the BCM is asleep, measure the parasitic current draw and start pulling fuses

Just because your battery is 5 months old, doesn't mean it's good... it could still have a bad cell from the factory

You should see 12.5-12.6 from a good battery after it sits for a little while (not 12.7 - 13.2)

If you have jump started the car in the past (especially recent past), I would not be surprised at all if you fried the BCM and need a new one

BBEngineer

 

Thanks for the update on the battery voltage BB....both my optimas were in between 12.7 and 13.2 volts right out of the box but maybe thats an exception. I still think your battery is the issue with the problem you are having especially after your vehicle starts right up with a jump. Personally i never had any issues with my BCM burning up after getting jumped but i guess it could happen expecially if you reverse the jumper cables by mistake. The owners manual for the Monte Carlo does show the proper way of jump starting the car and it does not mention anything about BCM damage if done so. Take back your 5 month old battery to the place where you purchased it and tell them it has a dead cell or 2 and is not holding a charge....let them do an exchange for you and get a replacement. As far as the alternator is concerned....i think you got taken on that one.......the only part inside your alternator that would kill your battery would be the regulator which is built in but i never saw it kill a battery while the engine wasnt running...usually when the regulator goes...you will not be charging the battery when your engine is running...you will be running on battery power only but if you have the complete cluster with the volt meter in your dash....you will see your gauge in the negative side of center and you will see the alternator is not charging when the engine is running and maybe get a battery light as well...Get a battery exchange and go from there.

 

I went to three different places today to get my battery tested alone, with testing the dead cells and came out good from all places. I got my battery from AAA but will go and try to exchange and see what happens.

 

Standard chemistry auto batteries (Lead-Acid and AGM IIRC) are 6 x 2.1V cells, yielding a 12.6V resting voltage

Other chemistry (GEL, etc) have different resting voltages

As far as jump starting, it's a pretty well know issue that the BCM is VERY fragile and is easily broken, especially when jump starting. Of course it's not in the owners manual, would you expect GM to disclose a design flaw in the owners manual?

If you battery tested good under load, then it's probably not the battery...

The most common culprits in these cars for parasitic draw are the factory radio, the factory amp, and the BCM. I have also seen ignition switches on the W-Body that are on their way out (due to arcing) cause battery drain as well. You can disassemble the switch (not the cylinder) and clean the arcing.. then reapply some dielectric grease and see if that helps

I would do the parasitic draw test again with an ammeter using the procedure I described (wait for the BCM to go to sleep) and then start pulling fuses. If you did indeed jump start the car and are now seeing these draw issues, it wouldn't surprise me if your BCM is fubar

Also, the battery cables on these cars tend to loosen up from vibration. Make sure the battery cables are tight (do NOT over tighten) and corrosion free.

BBEngineer

PS: The only way an alternator can cause the battery to drain is a shorted diode or fried regulator... and you would have known if that was the issue... Sounds like you went to shops that weren't too familiar with the oddities of the 00-05 Chevy W-Body and too lazy to do the actual diagnosis. I'd bet your original alternator is just fine