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post #16 of (permalink) Old 01-15-2019 Thread Starter
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Quote:
Originally Posted by Bill58 View Post
Ignore post. BCM goes to a bunch of fuses.
Tried to upload bcm pdf schematic but didn't work, sorry.
your right Bill,,, BCM module is connected to 6 other fuses,,,
i'll pull them tomorrow and remeasure parasitic drain.
JT,,, No modifications or ad-ons that i am aware of, owned for 4 years.

thanks
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post #17 of (permalink) Old 01-16-2019
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Let me look for some drawings of the BCM, and I'll post something tomorrow
I pulled some BCM drawings together. The data is for 2009, but it should be the same on your 2007.

Below is a brief summary of the drawings. Start on page 1.

There are many things to consider in all this. I'd start by pulling the 2A fuse that feeds the steering wheel. It's tapped off the 10A BCM fuse. You want to see if that affects the current.

Doug

Page 1 shows the 10A BCM fuse. It feeds the BCM, the ignition switch, _and_ the theft deterrent module.

Page 2 shows several fuses feeding into the BCM.

Page 3 shows BCM X3-18 going to interior lights dimming circuit on page 8.

Pages 4-7 show the many signals connected to the BCM.

Page 8 - see page 3 above.

Page 9 shows several lights connected to BCM.

Page 10 shows the theft deterrent connections for the BCM.
Attached Files
File Type: pdf 2009_impala_bcm_stuff.pdf (687.4 KB, 20 views)
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post #18 of (permalink) Old 01-16-2019 Thread Starter
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wow,,,, looks like BCM module goes everywhere
thank you,,, i'll see where it takes me,,, easiest will be to pull fuses,,,

i dont think i'll be able to probe the BCM module itself,, due to it being under dash (my old body wont go there)
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post #19 of (permalink) Old 01-16-2019
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Originally Posted by deadimpala View Post
wow,,,, looks like BCM module goes everywhere
thank you,,, i'll see where it takes me,,, easiest will be to pull fuses,,,

i dont think i'll be able to probe the BCM module itself,, due to it being under dash (my old body wont go there)
I got a few minutes to ponder the drawings. Here's a few more thoughts on the subject.

Things to fiddle with.

1. Fuses in underhood fuse box (page 2) feeding BCM. Appears to be 6. Not sure what effect these will have. Frankly, pulling one should cause some sort of alarm condition in the BCM - ie, if it affects the BCM current, I'd expect it to go up, not down.

So what I'd do is pull each one and ohm it out to be sure they're all good and hence feeding proper voltage to their respective BCM pins.

2. On page 3 in the upper right corner, the BCM goes to the "interior lights dimming circuits". I'd fiddle with the dimmer knob while monitoring the BCM fuse to see if the current changes any. My half-baked thought is that maybe something's wonky in the dimmer causing extra current to be drawn. That said, it's not clear if the BCM watches this pin, X3-18, or only pulls it low when it closes the switch.

3. Following that same wire, it goes thru the 2A STRG WHL fuse in the underhood fuse block to the steering wheel. Again, it's not clear how or if this path affects the BCM, but I'd pull that 2A fuse (as mentioned previously), and see if the current in the 10A BCM fuse changes.

4. Page 4, pwr_and_gnd, is mostly a rehash of page 2, but notice that the ignition switch taps the 10A BCM fuse in three places. One of those is the key detector circuit. So I wonder if that little doololly in the side of the lock cylinder could be contributing to the current draw. (I think it's a Hall effect sensor that detects the presence of the metal key, but not positive.)

What I think should also be done is to get an ammeter in series with the 10A BCM fuse in order to get a more accurate reading, then monitor that as you perform various tests.

[Edit]
Quote:
Measures .6mv across fuse ,,, according to charts drawing around 75ma constantly.
Thinking about this some more, with a car battery typically having something like 80 amp-hours of capacity, at 75mA, you'd have to leave it parked for something like 44 days to run it down. Even 20Ah would take 11 days. That is, if it's only drawing 75mA, but it's killing the battery in a short time, maybe the battery is part of the problem.

That said, as suggested above, if you can get a ammeter inline with that fuse, it will give a much more accurate indication of the actual draw.

HTH.

Doug

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Last edited by plano-doug; 01-16-2019 at 07:22 PM.
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post #20 of (permalink) Old 01-17-2019 Thread Starter
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Doug,,, thank you for calculation,, yes i calculated the same rate of battery discharge,, over a month. Problem is compounded by fact car is only driven 2 miles twice a day,,,, the battery seems to lose 50% of its charge after 2 weeks ??? Battery was tested and replaced twice,, no change.
Alternator does charge at proper voltage (over [email protected]) and does charge-up battery when driven more miles. Never had this problem before with low battery!!!
Thinking further,,,, maybe i'm getting additional battery drain from (defective) alternator too ??
,,,,would a leaky diode still charge battery normally ??
but i still have 75ma constant drain on the BCM fused circuit 1.8A/dayX30=54amps/month !!!!!
and car wont start with very low battery,,, may actually be fewer days than calculated.
Had the car in shop,,, mechanic did verify, but could not identify problem causing low battery,, maybe electrical not his specialty ??? ,,, told me hes been working on cars for 25 years
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post #21 of (permalink) Old 01-17-2019
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Originally Posted by deadimpala View Post
Doug,,, thank you for calculation,, yes i calculated the same rate of battery discharge,, over a month. Problem is compounded by fact car is only driven 2 miles twice a day,,,, the battery seems to lose 50% of its charge after 2 weeks ??? Battery was tested and replaced twice,, no change.
Alternator does charge at proper voltage (over [email protected]) and does charge-up battery when driven more miles. Never had this problem before with low battery!!!
Thinking further,,,, maybe i'm getting additional battery drain from (defective) alternator too ??
,,,,would a leaky diode still charge battery normally ??
but i still have 75ma constant drain on the BCM fused circuit 1.8A/dayX30=54amps/month !!!!!
and car wont start with very low battery,,, may actually be fewer days than calculated.
Had the car in shop,,, mechanic did verify, but could not identify problem causing low battery,, maybe electrical not his specialty ??? ,,, told me hes been working on cars for 25 years
I agree, 30 days at 75mA is 54 amp-hours, enough to kill many batteries.

I think you're on the right track with the BCM fuse. The remaining challenge is to narrow it down from there.

As for "electrical not [being] his specialty", my observation is that, for many, electricity is black magic Civil engineers think electrical engineers are spooks. And electrical engineers think RF guys are spooks Throw in some encryption, and it gets really scary

Seriously, I was never comfortable with it until I got some rigorous schooling in college. Prior to that, everything was a hodge-podge of fuzzy terms - AC, DC, rms, peak, average, continuous, balanced, unbalanced, etc.

So it's understandable that your guy may not be real comfortable with it.

Back to diagnosing the parasitic draw, the challenge at this point is that it becomes tedious. With each test - each removal of a load by pulling a downstream fuse or removing a bulb - the quiescent 75mA load may jump to a different level, either higher or lower. Before you can move to the next text, you will need to re-establish the 75mA draw, which may take a few steps and several minutes of waiting. So it can take a while to narrow it down to the source.

Of course, if you see the 75mA draw drop way down when you remove a load, then you may have found the problem. So perform that test again to confirm it, then shout "eureka!"

In short, it can be a grind going thru this looking for the culprit. Some of the hi-end test equipment at the dealer may be helpful. For example, it may be able to communicate with the BCM to find out what's keeping it from dropping to its lowest current draw - ie, going into standby. Most ordinary scanners won't be able to do that. So you're left with disconnecting cables, bulbs, etc, until that 75mA goes away.

That said, I think you're pretty close to finding it. So I encourage you to keep looking.

HTH.

Doug

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post #22 of (permalink) Old 01-17-2019
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Hey everyone, just wanted to let you all know that all this information has been of great use to me. I am currently on the same boat and struggling to figure out the problem. However, my vehicle is randomly draining the batter over night and not over and extended period of time. I do believe my problem may be related to my stereo. Suddenly, there is no sound from the speakers while stereo is on. I've pushed all the buttons changing the stations and going through different functions of the head unit and nothing comes out of the speakers. The next day after this happens, the battery is dead. After jump starting, the vehicle runs as normally would and stereo works just fine. Any ideas as to what this may be?

Thanks!!
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Originally Posted by GorditoSS View Post
Hey everyone, just wanted to let you all know that all this information has been of great use to me. I am currently on the same boat and struggling to figure out the problem. However, my vehicle is randomly draining the batter over night and not over and extended period of time. I do believe my problem may be related to my stereo. Suddenly, there is no sound from the speakers while stereo is on. I've pushed all the buttons changing the stations and going through different functions of the head unit and nothing comes out of the speakers. The next day after this happens, the battery is dead. After jump starting, the vehicle runs as normally would and stereo works just fine. Any ideas as to what this may be?

Thanks!!
What year is your car? Is the head unit stock? Or aftermarket? Is there a factory amp under the rear package try? Did you install an amp?

My first guess would be the amp, aftermarket or factory, is not shutting off when the car does.

Another thought was bad ignition switch. But that doesn't explain the radio not playing when the car is on. Still, I don't want to rule it out yet. A bad switch could have one circuit staying open when it should be closed (-> no sound because no power to amp), or staying closed when it should be open (-> dead battery). I would need to look at some drawings to drill down on this.

Still another thought is wiring. I would inspect any wiring in the rear deck first (where the factory amp is). Look for a loose wire at the connectors or a chafed wire in the area. The idea is that the wire that turns the amp off and on has an intermittent connection or is shorting to ground.

After that, you would need to pull the head unit to inspect the wiring there.

In short, since the radio seems to be misbehaving in conjunction with the dead batteries, I think you're on the right track focusing on the sound system.

Doug

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Last edited by plano-doug; 01-17-2019 at 09:43 AM.
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post #24 of (permalink) Old 01-17-2019
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RF guys are spooks

Yes, yes we are. Thanks for noticing
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post #25 of (permalink) Old 2 Weeks Ago
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I had to take my fuse for my radio out it was drawing like 2a..now I'm down to 79ma being drawn from somewhere I took my display fuse out and it went down to 30ma.. i was going to try to ride with that fuse out..I realized none of the gauges work with that out...Has anyone heard about a radio drawing that much..No aftermarket stuff I have a 06 ss with the Bose system kind of getting tried of riding without a radio
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Originally Posted by Alanb View Post
I had to take my fuse for my radio out it was drawing like 2a..now I'm down to 79ma being drawn from somewhere I took my display fuse out and it went down to 30ma.. i was going to try to ride with that fuse out..I realized none of the gauges work with that out...Has anyone heard about a radio drawing that much..No aftermarket stuff I have a 06 ss with the Bose system kind of getting tried of riding without a radio
When the radio is off, the only current it draws is for keeping the presets alive and the clock running (w/o display). That takes like 1uA. Call it 10, worst case. So it should be a very tiny draw. BTW, 10uA=0.01mA . Depending on the meter, it might not even show up.

Keep in mind what's been posted earlier in the thread. After making a change, you may need to way a few minutes for everything to die down so you can get the actual standby current.

Doug

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