Parasitic Loads

batteries

#1

2000 GMC Sierra 1500, 5.3L. I can’t let it sit more than a week or the battery is dead. Testing with a DMM, I get about 700mA of draw after closing the door and before the interior lights go out. After the delay and the lamps go out, it drops down to around 230mA, and stays there. If I started pulling fuses, the IGN is about 10mA of it, the Courtesy Lights are about 150mA of it, and I can get rid of the last 70mA by pulling the BCM fuse. Pulling the BCM fuse before the Courtesy fuse takes care of all 220mA.



I have tried to eliminate the Courtesy fuse draw by unplugging both door harnesses and unplugging the harness in the headliner, but no luck. Even if I can find this, the BCM still seems too high. Everything I have read says I should be in the 25-35mA range once everything has settled down, and certainly not more than 50mA.



Any ideas?



Thanks


#2

First give it about an hour to get down to steady state. Then measure the amps.

How old is the battery? Have you tested the battery or the charging system? What is the voltage with the engine running and with the engine off?


#3

Got OnStar?maybe it is wired wrong,it does have a constant power connection


#4

Could a light be stuck on in the glove compartment, under the hood, or anywhere else not immediately visible?


#5

Under hood light you are forgetting? What exactly is the BCM? Does it have an alarm system or remote starter?


#6

As Nr, Meehan asked; what about the battery? If that’s the original then it’s been on borrowed time anyway because it’s now probably more than 9 years old.
(assuming production date of the truck was summer or fall of '99 and the battery was manufactured before that.)

Disconnect the battery negative cable, and while shielding the battery post to provide some shade, lightly touch a sharp corner of the cable end to the battery post.
If you see a noticeable blue spark then the draw is enough to worry about. A faint yellow spark genereally means it’s not.

Likewise with a test light. A brightly lit connected between the battery post and cable end means a voltage draw of concern and a very dim test light means no worries.

That’s not real scientific, but it works. If the battery is suspect it might be better to just replace it because some of the load testing methods I’ve seen used are a bit debateable. Hope some of that helps.


#7

I don’t understand why courtesy lights should be drawing anything after you give them time enough to go out. Your biggest problem is the Courtesy lights circuit, not the BCM. It draws less current and is more understandable. I think you have a parasitic load problem and a weak battery. A week at 0.230 amps is 40 Ah. You should still have enough juice in a good battery to start the truck, but the constantly discharging battery has been weakened.

80 mA is probably not too far from what you should have though I would like to see it a bit lower. For a large sedan, 50 mA is more reasonable. Do you have a wiring diagram?


#8

This might give you an idea: http://www.aa1car.com/library/battery_runs_down.htm