02 Tahoe battery drain issue.

[rickp]

Hey guys, not sure if this is the right place for this. If not please move to correct section.

 

My 02 tahoe has had a battery drain issue for a while now. initially it started with the battery going dead after a week or so of no driving. At the time my ignition was going bad so I thought there was a short in the ignition causing the battery drain. I just replaced the ignition but the drain is still there. Now this is the twist and the biggest clue, at least to me, even though thats not saying much. whenever I turn the ignition on and the truck starts, the headlights automatically turn on as well, I know this because the dash lights and the PRND123 dim as they always have when the lights turn on. Before the issue, the headlights would only turn on at night by the ambient light sensors. Now since the headlights always turn on, no matter what, I have to manually turn them off by pressing the button on the light control switch on left side of the dash.

I have pulled all the circuit breaker's under the hood that control the headlights and lamps that i know of, but the dashlights still dim when I start the truck, (no light turn on)
So what controls the dash lights, or the signal from the ambient light sensors to the dash.
BTW, I've replaced 1 ambient sensor (left one) cant reach right one without removing dash, and the headlight control switch.
Could this be a clue as to where the drain is?

Thank you for any help.
R.

[The Zip]

rickp - I have a 01 Tahoe and yes that is how the lights come on, but the fact that they come on with the engine running should not have negative impact on the battery drain (still may be some other gremlin causing an issue), there would be a problem if they come on when the engine was not running. Check your alternator belt for cracks and flexibility, too much of either will cause your alternator not to charge the battery. Also the alternator is not off the hook. Your battery should not be dead after sitting just a week or so. Also, how old is your battery, you didn't mention. Colder weather hits an older battery pretty hard. Eliminate if your battery is holding a charge before you try to figure why it's being drained.

[rickp]

Thanks Zip for the reply. Actually I made some headway today. First off the battery was bad so I had it reaplaced. I also had them check the alternator and it came back good. The bad news is the ALC is still not working right. Time will tell if this is a drain or it was just bad timing on both issues coming up at the same time.

 

After I got the battery I did a drain test with a multimeter and pulling all the fuses out one at a time. Nothing really jumped out at me. The multimeter showed a constant drain of .25A. once things settled after locking the doors with the security fob. The amps did jump to 1.5A when I removed and reinstalled the TBC fuse but after a few seconds again settled to .25A. When the fuse was out the amps dropped to .01A

 

What I did find out though is that I got a DTC code B2647 which is a Ambient light sensor code, which expalins the issue. Now I need to find out if I can fix that or need to replace the BCM.

 

Again thank you.