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parasitic drain? 2002 Sierra 1500

trouttrooper

trouttrooper

Big Blocks ROCK!!!
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Hoping to get some insight from someone smarter than me. 2002 Sierra 1500 4x4 w/ 5.3, 310,000 miles. mechanically this truck still runs amazing, everything still works, and no rust. I've owned it for about 4 years now as a "first time" vehicle for my kids. I've been tinkering/fixing some minor things before I hand the keys to my next kid. oil leaks, bad o2 sensors, broken plastic pieces here and there etc. I've been driving it off and on the past 4 months listening for any issues that need addressed, when a couple weeks ago I went to start it and it was dead. I mean dead dead. battery was less than a year old. got it to take enough charge to hold above 12 volts. drove it around then went through all the fuses testing for voltage drop. didn't find anything. got a new battery, tested fuses again for voltage drop, again nothing. 2 days later go out and it's dead again, sitting at 5 volts. got it to take a charge so it holds above 12 volts but of course my battery tester says it's only able to produce 300 CCA now. drove it last night and noticed the volt gauge on the dash was over 14 volts. put a meter on the battery and it reads 14.7 and doesn't fluctuate when I load and unload the electrical system while the engine is running. my charging tester also said its too high, so I'm thinking bad alternator overcharging, but would that kill a battery within 2 days? can an alternator be a parasitic drain when the engine is off? no check engine light or any codes using my bluedriver code reader. I don't see any obvious loose cables or wire corrosion anywhere.
 
with a battery drain issue on top of high voltage charging I want to say the internal regulator in the alternator is hung. use a test light in between the negative batt cable and the post disconnecting the negative on the battery and using the test light to go between the cable and the post on the battery. close all doors and make sure the key is out of the ignition. if the test light is bright, the first thing I would try is to remove the large positive wire off the back of the alternator and the small connector and see if the test light goes dim. it will normally remain dim with the "keep alive" power to the radio and the ECM.
 
trouttrooper said:
it reads 14.7
Click to expand...
That's under 15V. Depending on temperature it's fine. Unless the battery stinks and/or is boiled dry ... again FINE. OT the 2002's had a TSB to move the alternator "sense" wire to the output of the alternator as it would "ring" with noise during a shift and confuse the ECM. This change removed the ability to compensate for voltage drop during heavy current on the charge wire.

Offhand battery drain could be:
Brake light switch.
Bad trailer brake controller, aftermarket.
Underhood lamp stuck on. I forget what lamps are controlled by the BCM battery saver.
Horn going off , does the horn actually work? Horn relay silently killing battery if the horn is INOP.
OnSuck now forever looking for an analog cell tower that's no longer out there.

Make sure you have pulled the fuses for OnStar a known battery drain. It's INOP due to being obsolete anyway.

Last check the vehicle at the coldest time in the AM for brake lights being on, horn going off, other lights on.
 
Overcharging from a bad alternator can indeed kill a battery faster than usual. It might not always throw a code, but it could act like a parasitic drain when the engine's off, especially if it's malfunctioning.
 
Well to add insult to injury, I had a 4-amp battery maintainer connected since Wednesday night. The display showed it was charging and doing its job that night. Checked it the next morning and it was still showing good. Tonight, I go out and it's flashing its error code, the battery is completely dead, and unable to take a charge. Something is draining it faster than the maintainer can overcome. I'm waiting for better diagnostic tools to arrive, my amp clamp quit working a while ago and I never got around to replacing it, and also get a new battery. Of course, I have all sorts of time to work on this little project, it's not like I have a regular job and also building a small addition to my house this summer.... oh wait, I am 🤔.

I will post results here when I figure out what's going on.
 
WarWagon said:
That's under 15V. Depending on temperature it's fine. Unless the battery stinks and/or is boiled dry ... again FINE. OT the 2002's had a TSB to move the alternator "sense" wire to the output of the alternator as it would "ring" with noise during a shift and confuse the ECM. This change removed the ability to compensate for voltage drop during heavy current on the charge wire.

Offhand battery drain could be:
Brake light switch. - I have checked it, doesn't seem to be malfunctioning
Bad trailer brake controller, aftermarket. - doesn't have one
Underhood lamp stuck on. I forget what lamps are controlled by the BCM battery saver. - been unplugged since I bought it, never trust them to turn off, lol
Horn going off , does the horn actually work? Horn relay silently killing battery if the horn is INOP. - horn works, never hear it go off on it's own
OnSuck now forever looking for an analog cell tower that's no longer out there. - didn't know that was an issue, I'll pull that fuse regardless, thanks!!

Make sure you have pulled the fuses for OnStar a known battery drain. It's INOP due to being obsolete anyway.

Last check the vehicle at the coldest time in the AM for brake lights being on, horn going off, other lights on. - nothing detected
Click to expand...
 
I have a battery maintainer I bought at napa and it will do the same thing on a good system. You have a large draw to run down the battery that fast. You really need to follow that parasitic draw test Will linked for you.
 
If you get a cut on your leg do you drink some water trying to stop from dehydrating and to ensure your body can continue to produce blood? Or so you examine where the blood loss is coming from and stop it?
 
I'll definitely do a parasitic draw diag as soon as I have the correct tools. the only multimeter I have left that's halfway decent can't measure amps. the only test I can do until then is measure voltage drop across the fuses. not the best way to test, but a large power consumption should be detected, which I don't see across any of the fuses under the hood or inside. that is why I was starting to wonder if it's the alternator, since I can't currently test it with what I have other than voltage output when running. that test says it's putting out around 14.7 volts regardless of what kind of load I introduce.

once my new and improved multimeter and amp clamp get here I'll be in better shape to diagnose.
 
That sounds like it could be your alternator overcharging and messing up the battery. I had a similar issue with my old truck where the alternator was sending too much voltage and killing the battery. I’d try swapping out the alternator and see if that helps. Also, double-check for any hidden parasitic drains with a multimeter just to be sure.
 
trouttrooper said:
14.7 volts regardless of what kind of load I introduce.
Click to expand...

Alternators change voltage depending on temperature AND voltage drop on the charge wire to the remote voltage sense wire. Load doesn't change the commanded voltage by design to the limit of the alternator at idle speed. My 2003 Dodge Cummins ran 15V and had the least amount of battery failures Vs GM's lazy float charge voltage of 13.5V. (The Massive draw of grid heaters or glow plugs would overcome the alternator current limits though.)

I question the accuracy of your voltmeter. Is it reading around 12.6V on a battery that has sat overnight with no load including dome lights put to it?

Unhook the alternator and tape the charge wire up overnight if you suspect it's draining the battery. A test lamp lighting up between the charge wire and alt charge terminal would show you if it has a shorted diode draining the battery.

Park it away from things that burn as a drain this large could completely short and burn the truck down. After all GM Has the Original Blazer! In fact parked with battery disconnected is smart till the proper tools arrive.
 
currently it has no battery in it since it is completely dead and won't take a charge. it's sitting on my bench until I go to the store.

I would argue my meter is fairly accurate. it shows around 12.3 to 12.7 when testing all my other vehicle batteries when I test the alternator output on my trailblazer and silverado I can watch it hover around 13.5 to 14.0 ish and can see the subtle fluctuations on the display when turning on and off ac or headlights. this alternator however goes right to 14.7 and doesn't budge.
 
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