1997 Q45 Battery Parasitic Drain

[fontana dan]

Hello Forum,

I've been dealing with a mild parasitic drain on my battery for at least 2 years now. I'm not sure exactly when it started; I only noticed it when I began to let the car less. It's spanked my battery a couple times now so I decided to give it a quick diag.
Car parked, ignition off, key out, all doors and trunk closed, hood switch unplugged; current draw sits at 200mA. Let the car sit for 30+ minutes and it does not change.

Through some investigation I found that the current draw goes away only if you pull both 40A fusible link "h" labelled "Power Window" under hood and 7.5V fuse #14 labeled "BCM" in interior fuse block. Draw goes to near 0.000 amps at that point. With fusible link "h" in place, I see almost no measurable drop across fuse 14. With fusible link "h" removed, I'm looking at about ~1.5mV of voltage drop across fuse 14. With either fuse in place, the current draw is immediately restored.

Looking at the schematic it seems those two supply battery voltage to the BCM and the rest of the LAN. I wonder is it a fault with the LAN system unable to enter sleep mode? Would anyone be able to tell me what their Q current draw sits at before it goes to sleep?

I'm gonna try to run the self diag on the BCM. If that doesn't give me any direction, then I will have to let it be and continue disconnecting the battery if I plan on letting the car sit for more than 5 days.

[VStar650CL]

Fusible link H supplies just about everything in the window system, and if something in the window LAN is preventing the BCM from sleeping, you may not see a result until H is pulled with 14 left in and you wait 30 minutes. Keep in mind that the BCM will never fully hibernate if it thinks doors are open, so pull the driver's door switch while doing diag. If the draw persists after 30 minutes with H removed and no door switches active, then it's likely the BCM is faulty. Some of the older BCM's draw close to 40mA (as opposed to more modern ones which usually draw under 15mA), but 200mA definitely means the BCM isn't hibernating. If you get normal hibernation with H pulled, start looking at your window and sunroof switches.

[fontana dan]

Hey VStar. Thanks for the input. The 40A fusible link kind of let me down a rabbit trail with my eyes crossed looking at a bunch of wiring schematics for power windows and such. I think I've got it figured out now. No parts required!

I used "On-Board Diagnosis Mode II (Switch Monitor)" to determine that the trunk lid key cylinder switch was inoperative. I unplugged it, closed the trunk and the battery drain went away. Come to find out the switch simply wasn't fully latched onto the back of the key cylinder and stuck in "unlocked" position.
Now I can stand at the hood with all doors closed, depress the hood switch and observe the current draw immediately drop from ~200mA to somewhere around 10-20mA (I'm using a s*** multimeter). This confuses me a bit as well because the FSM specifically mentions a timer being involved with sleep function. I will try this again after driving the car.

Pictured below is the key cylinder on RH side of trunk lid. Going through the entire schematic on Mode II for BCM and LCA inputs and I'm surprised to find only two inoperable switches. (trunk key and drivers seatbelt buckle). Apparently this car is supposed to have a seat belt dinger? Who knew.

[VStar650CL]

Good work!