Battery discharge, voltage leak?

[dhspring]

My 95 Olds LSS has developed a condition where the battery is discharging while the car is sitting. It's not my alternator, it's pumping out 14+ volts and I've had it checked twice and it checks out okay. While sitting, the battery is discharging slowly. When I start the car my volt light comes on at the dashboard for a few minutes until the battery gets above 12 volts then it goes off. There are no lights on that I can see which could be draining juice. There must be something open or wired hot that is draining my juice. It is not the battery either, this is a brand new battery and it happened on the previous battery also which was new. Could the starter be pulling juice while off? I'm lost, any ideas by anyone? How do you check for something like this without going to the dealer?

Thanks!

[BNaylor]

It looks like you are getting some sort of parasitic draw/drain that is too high running down the battery. The proper way to check it is to hookup a special grounding bar to the battery negative terminal which has leads for a multimeter in the current position.

Look at your battery's reserve capacity rating. Take that figure and divide by 4.

For example if the battery reserve capacity is 100. Divide by 4 = 25mA.

If the draw exceeds 25 milliamps then you'll need to troubleshoot and find the source. A lot of the electrical has a constant battery 12 volts to include the starter even with the ignition switch to off.

A GM service manual with wiring diagrams would be helpful to see what electrical components could be the cause. Disconnect each through the process of illimination or until the parasitic draw is normal.

Typically shorted starters, body control modules, anti-theft deterrent, and power train control modules have the most current draw but it should not exceed the figure determined.

[dhspring]

Thanks Bnaylor, that's what I figure as well, a parasitic drain, but I'm afraid this will have to go to the dealer, I wouldn't think it would be too difficult for them, but would be for me, these are like looking for needles in a hay stack. Thanks again

[BNaylor]

Originally Posted by dhspring

Thanks Bnaylor, that's what I figure as well, a parasitic drain, but I'm afraid this will have to go to the dealer, I wouldn't think it would be too difficult for them, but would be for me, these are like looking for needles in a hay stack. Thanks again

You're welcome. The dealer should have the special tool (grounding bar) and hopefully has a good experienced automotive electrical tech that can pinpoint the problem in a reasonable amount of time since electrical labor costs at a dealer can be high. Good luck!

[Slade901]

You might be getting 14volts but not enough amps by your alternator. Have your alternator and battery tested by Autozone for FREE. You don't have to remove the alternator and battery anymore. They can check the alternator and see if it is providing a steady amps and battery still good with load test.

[HotZ28]

Before you take it to the dealer, you can do some testing on your own. It is very simple to track down a battery drain problem; you first need to see the drain. Your tool could be either a volt meter or you can construct a light bulb with two leads so that it will glow when there's electricity flowing.

Procedure:
1. Disconnect the negative battery cable from the battery.
2. Wire the two leads of either the voltmeter or light bulb tool between the disconnected battery cable and the negative battery post. You should see the battery drain at this time on the voltmeter (or see the light bulb tool lit).
3. Pull the fuses in the car one at a time, and observe if the battery drain stops. When the drain stops, you've found the problem circuit and need to investigate why.
4. If you've pulled all the fuses and saw no change, the problem circuit may be one with no fuse in it like the alternator or starter circuit. You would need to disconnect them manually to test.

[BNaylor]

Originally Posted by HotZ28

2. Wire the two leads of either the voltmeter or light bulb tool between the disconnected battery cable and the negative battery post. You should see the battery drain at this time on the voltmeter (or see the light bulb tool lit).

Interesting procedure Bo. Have ever seen a car with normal parasitic drain light the test lamp when connected in series with the battery ground? Or does it light only when there is abnormal drain or current flow. And if it does light do I have a problem. From past experience I found the light bulb test to be unreliable. I just tried it out on an Olds Alero and two Buick Regals and the lamp glows quite nicely. Using a standard 1157 lamp with leads soldered on. However, none of the cars mentioned have starting or charging system problems. Try it and you'll see what I mean. Just my two cents worth.

[BNaylor]

BTW - The special tool/equipment I mentioned earlier is called a Disconnect Tool (Shunt) GM Part # J38758 and works the best. If you don't believe me ask GMMerlin.

[dhspring]

Thanks to all for the advice, I'll see what I can come up with. I did have Autozone and OReilly both check the alternator, and they both said it was okay, I was hoping that was it, as that's about a 30 minute job and a hundred bucks to swap out an alternator. I'll post the problem and solution when I find out what it is.

[HotZ28]

Originally Posted by bnaylor

BTW - The special tool/equipment I mentioned earlier is called a Disconnect Tool (Shunt) GM Part # J38758 and works the best. If you don't believe me ask GMMerlin.

Bob, I never doubt anything you say and I have seen the J38758 disconnect tool made by OTC for GM. I just could not justify 85 bucks for something that I don't need. I will try to answer your previous questions and expand somewhat on my previous post with some test I conducted on two Buick's in my driveway today. (Finally had some spare time)! By the way, neither of the cars is suffering from “parasitic battery drain”.

Now, several items that come to mind that are notorious for causing battery drain are the ELC, power radio antenna (check to be sure it goes all the way down), glove box light, power door locks, blower control module, and of course the RAP/BCM. The following is considered to be normal drain items on these cars and the total should not be over 19.85 mA according to the service manual.

Adaptive Lamp monitor = 0.5 - 1.0 mA
HVAC Programmer = 0.5 - 0.75 mA
Gages Cluster = 4.0 - 6.0 mA
Oil level module = 0.1 mA
Radio = 7.0 - 8.5 mA
Amplifier = 1.8 - 3.5 mA

Total = 13.9 to 19.85 mA = 0.02 A max.

First, before I conducted this test, I grabed my 12V portable light with a built in cigarette plug socket. I plug one male end into the 12V light battery source and the other male plug into the cars cigarette lighter plug. (You can also do this with a 9V battery wired to a male cigarette plug) This provides a memory saver feature that protects the vehicle’s computer memory, preserving stored fault codes, drivability parameters & programmed electronic settings such as clock, radio, seat position, etc. The vehicle computer remains in "sleep mode," allowing correct parasitic drain to be measured. The test can be conducted without this feature, however I don’t like resetting all the radio stations (AM-FM1-FM2-FM3) & the clock.

When I tested my car, (no problems with drain) it drew ~ 11.50 milliamps when I bridge my multi-meter between the battery and the negative cable with all systems off. When using the 1156 test bulb, it is off. If you turn on the ignition switch, the light will glow, however not full bright. (The ignition components are drawing current through the test bulb)

If there is an abnormal drain, the test light will light somewhat, but may not be bright. Make sure the key is off and the doors are closed before conducting this test.
If the light is lit, you are now ready to start pulling fuses/relays one at a time while watching for the light to go out. Also, you want to start with the main cockpit fuses first, but don't forget the other two fuse/relay panels.

The above procedure works fine for the DIY owners. Now, if you are like a friend of mine who operates a local high volume auto repair shop and probably deals with this on a weekly basis, there are other options. He recently bought a really neat dedicated “parasitic battery drain tester”, that cost about $190.00. It is made by OTC & includes the Memory Saver feature. Part #3382. I conducted a test with my method on several cars at his shop and my $6.00 light and meter gave the same results as his 190 buck tester! Boy was he pissed.

The pics below will show how the test is conducted;
1)Top L pic shows light being tested with full battery voltage (12.76V) Notice the bright light.
2)Top center pic shows light connected between the ground strap and battery ground, with ignition switch on. Notice the light is dimmer than with the full battery voltage, however it is on.
3)Top right pic shows the light connected the same as above, with ignition switch off. Notice, there is no light! No drain detected.
4)Row two pics #1 & #2 shows the Fluke 23 DOVM probes hooked between the ground strap and the battery ground terminal. When set on the 300 mA scale, the reading is 11.50 mA or .01 amp. This car does not have a drain, so this is normal.
5)Row #2 pic #3 is what I use to supply 12V through the lighter plug for a system memory saver function.
6)Row #3 pic #1 is a simple portable test light with a 1156 bulb that is used for this test.
7)The dice, frog and ducks are for your viewing pleasure.

[dhspring]

Thanks HotZ28, I actually rigged up my Radio Shack voltmeter as one guy said and was able to see the drain. It worked just like they said, placed it between the negative cable and started pulling fuses. Sure enough I saw the voltage increase about 0.4 to 0.5 volts when I pulled the fuse that was draining the battery. Naturally, it was on the "electrical miscellaneous" circuit. Well this is the circuit that runs the heating/cooling control module and the radio. I do not have a full circuit drawing from GM, but the cheapo depo manual from Autozone shows a generic drawing of the temp control panel. I did see the blower controller module that you mentioned, it is hot at all times, this could be the culprit. I have checked all lights, glove box, they all seem to be out, and the power antenna goes down as well, this would be easy to disconnect to see if anything is up with that. At any rate, I think I have at least isolated the circuit that is the problem. I guess now, I just have to start isolating one by one. Thanks again for the excellent help!

[BNaylor]

Looks like a good write up Bo.Thanks for the time and effort. I was just commenting that using solely a test lamp can give false indications therefore I don't use them anymore for troubleshooting parasitic drain especially on mid 90s cars and up. Also, GM specificies you can have up to 50 mA of current as parasitic drain and still have a perfectly normal electrical system.

I have a question. Why did you have to turn ignition to on to check parasitic load?

I was able to get the test lamp illuminated with ignition off. As the poster pointed out he found something in the HVAC system which is hot at all times and that is the case in other circuits too.

From what I know about GM HVAC systems, the hi-speed blower motor relay has a hot connection at all times regardless of ignition being on. The reason for this is because of the load the fan has in the hi-speed postion so it acts as a bypass and the blower motor will then work directly off battery power. Of course, we all know the blower should not be operating with ignition off and HVAC off but it has been known to happen indicating a problem.

BTW - If you have a manual HVAC system the blower motor resistor is a good starting point. For digital HVAC the A/C Power/Blower Motor Control Module.

[HotZ28]

Originally Posted by bnaylor

Looks like a good write up Bo.Thanks for the time and effort. I was just commenting that using solely a test lamp can give false indications therefore I don't use them anymore for troubleshooting parasitic drain especially on mid 90s cars and up. Also, GM specificies you can have up to 50 mA of current as parasitic drain and still have a perfectly normal electrical system.

I have a question. Why did you have to turn ignition to on to check parasitic load?

I turned on the ignition switch, simply to simulate what a load/drain would look like and how the light illuminated, but not full bright. If your light is lighting with all systems off, you need to hook the DVOM to the terminals to see what it is actually reading. The light test works, however the meter is better. I will conduct some further test today to see actually how many mA are required to light the bulb and report back. The fact that some systems are hot all the time, with the battery connected, does not indicate that there is a drain from those, only that they are hot!

I would think that if GM is saying 50 mA is acceptable drain, they did so in order to CTA! That is not normal and would require a hefty & powerful battery to allow the car to be parked (without starting) for a month and then start when you finally try. A new battery might survive this amount of drain for extended periods, however a three or four year old one, would likely be dead!

[BNaylor]

Originally Posted by HotZ28

I turned on the ignition switch, simply to simulate what a load/drain would look like and how the light illuminated, but not full bright. If your light is lighting with all systems off, you need to hook the DVOM to the terminals to see what it is actually reading. The light test works, however the meter is better. I will conduct some further test today to see actually how many mA are required to light the bulb and report back. The fact that some systems are hot all the time, with the battery connected, does not indicate that there is a drain from those, only that they are hot!

I would think that if GM is saying 50 mA is acceptable drain, they did so in order to CTA! That is not normal and would require a hefty & powerful battery to allow the car to be parked (without starting) for a month and then start when you finally try. A new battery might survive this amount of drain for extended periods, however a three or four year old one, would likely be dead!

Sounds good Bo. This thread will probably have the most comprehensive topic on parasitic load. The only other ones that comes to my mind is the Olds Intrigue subforum.

I agree on the 50 mA. I would not feel comfortable with that much parasitic load. From what I understand it depends on the battery's reserve capacity. If the reserve capacity is 120 then divide by 4 and the maximum draw should be no more than 30 mA. I have standard 120 reserve capacity batteries.

Just for annectodal info here is the range of parasitic load for a couple of key devices. I don't have time to list all components.

BCM module - 3.6 mA to 12.4 mA after the 20 minute run down period.

HVAC Power Module - 1.0 mA to no more than 1.0 mA.

[HotZ28]

Bob, I have to agree that this is the most comprehensive post on the subject of “parasitic battery drain” that I have ever seen. I really appreciate your input and questions, which help us clarify some of the common misconceptions people seem on have, on how to find a battery drain.

Well, I have some interesting updates after checking what “lights the light” on the same Buicks tested previously. My objective this time, was to generate enough “parasitic drain” to light the 1156 bulb and then measure the mV on the DOVM to determine how many mV are passing through the ground cable terminal, to the battery ground post.

As mentioned earlier, the same car measured 11.50 mA with all systems off and did not light the bulb at all. First, I decided to use the glove box light as the initial simulated drain on the system. The following pic #1, will show that the light barely lit, with the glove box light on. Reading on the DOVM at this drain measured 26.50 mV. I then opened the trunk, (in addition to the glove box) and checked the light again. It was somewhat brighter, (pic #2) and the DOVM measured 38.50 mA with the test light disconnected, the same way as measured in the previous test.

Just to add some additional credibility to my findings, I opened the door to allow the interior lights to come on in addition to the glove box and trunk light. At this point the test light was bright enough to use for an under-hood light. Meter reading was 88.67 mv.

Remember, with all systems off and no drain detected, this same car measured 11.50 mA yesterday. If you do the math on this, the additional 10.00 ma drain generated by the glove box light being on, did make the light illuminate enough to see! With the trunk light and glove box light combination simulated drain, I had an additional 27.00 mV and the light was bright enough to read by.
:22yikes:

So in conclusion, I have determined that the light test is accurate enough to detect harmful drain on the battery. Again, the DOVM is the best method for the DIY troubleshooter, however, the light test will tell you the same thing if you know how to read the illumination of the bulb. (The more the drain, the brighter the light, the less the drain, the dimer the light). Ideal situation is, no light at all!!