Battery drain/ BCM issue?

[Sackett2622]

Hi everyone, thanks for the great advice I've gotten here since I joined. I am combining my previous posts into one thread here, in hopes of getting all of the troubleshooting advice and help.

I have the following issue on my 2003 Yukon XL Denali.

1. Rear Access Open message on DIC. Rear hatch closes and locks properly.
2. Excessive battery drain (dead after 2 days), battery drain slows down considerably when I pull the Bose amplifier fuse.
3. Dome lights stay on (assuming because of the Rear Access Open error). I use the dome light bypass to keep them off.
4. To lock the truck, I have to push the Lock button on the fob one time, and then the interior lights go on, but doors don't lock, then I push the Lock button a second time and then all doors lock.

Everything, I have been reading here says, it can either be a bad lock switch/actuator on the hatch or it's the BCM.

I don't have a bi-directional scanner. Maybe my mechanic has one. What is the best way to go about troubleshooting these issues? How would the bi-directional scanner find some of these issues? What are the codes to look for?

Another question, I have is, if it is the BCM, how do I trust that another used BCM I get (like from car-parts.com) will be reliable and not have it's own issue?

Thank you everyone, for any and all advice. I bought this XL Denali used, 2003, with only 67k miles. Drives great! It has the blown rear shock air bags, but I'll fix that later with a Strutmaster conversion kit.

To make sure the BCM is completely going to sleep, when the vehicle is off, do the following; Unhook both battery cables from the battery. Leave them off over night. Next day, hook them back up. This should “teach” the BCM to truly go all the way to sleep when the vehicle is off, instead of partially sleeping and draining your battery. Also, unplug any accessories in your vehicle when parking it for the night, like phone chargers, etc. If the battery method does not work, you can take it to a shop and have them re-flash the BCM to reset it at a cost of around 200.00 If all else fails, replace the BCM. Good luck.

 

[Fless]

Cart before the horse... no need to condemn the BCM yet. These types of issues scream for a parasitic draw test to determine 1) how much the draw is; and 2) IF there is a parasitic draw, which circuit is causing it. Plenty of good YouTube videos out there on parasitic draw, and if you search for that term in this forum, there are many links to the videos.

After that, it's time to diagnose the actual circuit issue.

 

[strutaeng]

Thought I'd try to refresh this thread since I don't see a solution yet and I have some of the same issues and haven't found a closer post on here. I have issues 1, 3 and 4 above. I've had excessive battery drain in the past but solved that by removing PO's aftermarket remote start. My number one is Right Rear Door Ajar instead of Rear Access Open. The interesting thing on my vehicle is that the problems come and go for no reason! And they come and go together. I know when I get the Right Rear Door Ajar message that the interior lights won't work right. Also associated is the feature that keeps some accessories working for a short time after you turn the engine off (stereo, power windows) until you open the door. All these come and go at the same time. So, is it the door switch causing all of this? Or a bad ground somewhere? Or the BCM?

Ditto what @Fless said: first find the circuit that's causing the parasitic battery drain, then go from there.

However, it definitely is a clue that the door ajar may be causing issues.

My Mom has an 05 Escape and it had battery drain issues and the alarm would randomly go off in the middle of the night. She dropped it off and I monitored the amp draw and couldn't find anything. So talking to her she mentioned if she made a left turn the dome light would sometimes turn on and the door ajar message showed up on the cluster. A little internet digging I found the passenger rear door switch intermittently malfunctions randomly and it's a known issue. Even OEM replacements don't seemed to last based on reviews. So she gave me the go ahead to bypass the switch after I explained the drawbacks. Problem solved.

Not saying this is your problem, just an example. You can temporarily jump the circuit to isolate if it's a switch/wiring issue or the actual BCM.

Good luck.

 

[S33k3r]

This could help:
QUADRASTEER! GM Parasitic Battery Drain from the FACTORY? (Part 2)

 

[jhilario72]

I'm pretty sure the battery drain is the Bose amplifier. I checked the voltage across the 15A fuse for the amp, and it definitely was pulling a few hundred mA. Once I pulled the fuse the drain is gone.

I do have the Rear Access Open message still (which I have yet to diagnose if it's the Rear Liftgate/Liftglass switch or if it's the BCM).