LLY: Help! Parasitic battery drain problem

[ALLY Fox]

Been noticing the starter seemed to be dragging when I parked for a couple of days, I thought maybe the 12 year old starter was going out but decided to do some checking first. When I disconnected the batteries, the 2nd one drew a big spark so I checked and found out I had a 4 amp draw with nothing on and other battery disconnected. Started pulling fuses, relays and breakers one at a time while watching current draw, pulled every thing in the main fuse panel under the hood, in the MBEC block and the left dash block, nothing changed. The only thing I found that made a difference is if I pulled the INFO connector off the MBEC block and the current draw dropped to 2 amps. I believe that feeds the OnStar, not sure if there's anything else on that plug. Are there any other fuse blocks besides the main underhood, MBEC and left dash to check? Anybody have any ideas what else to check? Last time I had a battery drain problem it turned out to be the passenger seat fore/aft switch sticking, but not this time.

 

[Hoffie]

aftermarket stereo system or still the stock one?

 

[ALLY Fox]

Original Bose (works OK). I have some added things, like onboard air, lift pump & EGT gauge sender but I totally eliminated those circuits first thing. I haven't checked the 175 amp GPC fuse yet...

 

[Awenta]

Check all the grounds carefully


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[Awenta]

Add another. Even a temporary one and check again. Check all the main power cables for a rub


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[THEFERMANATOR]

Try removing the charge wire from the alternator. I've seen regulators get stuck on internally, and draw 4-5 amps.

 

[Budneeds2beers]

Hmmmm ive read about seat heaters having draw.... my tahoe has this issue. I dont think another ground would help Awenta. unless its a noise issue (like static draw) and if you dont have a ground then you cant complete the circuit (kirkoffs current law). It maybe rub but i would dought it just beacause other equipment would be running and easier to spot on. Also if it was a short to ground it would burn the wire or blow a fuse and even melt equipment. Good ideas but unlikely. Hey fermanator. Your saying the altenator? I would think it has some sort of diode to stop back flow. (Motor generator scenario) you would be able to ohm the alternator for a short. Let me ask a dumb question. Your lift pump isnt staying on is it? Its hard not having the truck in front of me to better help you. Glw this brother ill check back in and try to help.

 

[c20elephant]

Shot in the dark, when I replaced my alternator with a larger amperage output at idle I did not notice at the time that the wires coming out of the alternator where it goes into the main harness were chaffed and bare. I found it several weeks later while doing an inspection and digging around. This is one of the many problems I have found since purchasing my truck in 2013....

May want to do some digging around on the loomed wiring for chaffed wires which IMHO causes more problems on these aging trucks due to the piss poor wire management/retaining American cars/trucks use....

 

[ALLY Fox]

Thanks for the ideas and help everybody. One of the first things I did was disconnect the alternator to make sure one of the diodes wasn't shorted, no change. Also completely isolated the lift pump and air compressor. I also checked everything in the dark to make sure there were no lights on anywhere. I know sometimes the instrument panel can be a problem with developing shorts because of the lead-free solder, but pulling the DIC fuse would have eliminated that problem.

 

[BlkMax]

Do you have an autostart? They are great, but can cause issues with battery drain.

 

[Bustedknuckles]

I would actually unplug the cluster while watching amp draw. That is the only thing ive ever seen cause a battery drain on a silverado.

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[Awenta]

You've been towing your camper a lot recently right. Check the connections back there. I had the brake wire short once in the back of the plug.


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[CarolinaHD]

Unplug the blower motor resistor and see if the draw changes

 

[Budneeds2beers]

Any luck?

 

[whitetrash21]

Had a similar issue on my LLY. Had to be something body related though....had the truck torn down for headgaskets so ECM, TCM and GPCM were all unplugged. Hooked batteries back up after trucks as torn down so I could use the keyless entry to get in and out of it. It sat for about 2 weeks while I waited for parts and machine shop. Once I got everything back, I went to work on it and the batteries were far enough gone that the keyless entry wouldn't even work. Never did figure out what it was....

 

[ALLY Fox]

Any luck?

I had to walk away from it for a bit, had some other things that needed to get done and anyway, my fingers are sore from pulling connectors, fuses etc so hoping to get back to it today or tomorrow to check the blower resistor and some of the other ideas mentioned. Also trying to figure out where the "door open" switch is so I can override it while I'm checking fuses etc with the door open.... I'll let you know what it was when/if I find it.....

 

[testdrive]

Any lights on the instrument panel? Battery light or shift indicator?
Take a non contact thermometer and check for things that are above ambient temp. Be sure to check rear seat entertainment display in the back of the console. Radio, XM, Onstar, even door panel switchs. You can also use the back of you hand, just make contact

 

[Dan@PPE]

Check the ABS pump under the truck (drivers seat), disconnect the plug with the larger red and black wires on the module. recheck for current drain...

 

[ALLY Fox]

I think i found the problem! I was trying to set the door switch and it was sticky/gummy. Didn't seem to make any difference when I flipped it so I cleaned it up with some contact cleaner and exercised it several times, closed the door and waited about 12 seconds for the BCM to normalize and current draw went from ~4 amps to 80-90 milliamps, that's about what I would expect to see. I may have to replace the door switch but at least I'm pretty sure that's what was going on. Thanks for all the tips!! I will keep them in mind if this doesn't fix it.

 

[testdrive]

Hope you can get it down even more... 80 - 90 mils is too much. Keep that meter on for up to 10 minutes or more.