Parasitic Draw Help

ColtMk18 · Mar 30, 2014

A little background. I have a ’07 Colorado WT bare bones I4 5-speed 4x2 with nothing aftermarket except new rims and TPS sensors. It has 2250 original miles. It has sat in a garage every winter. 3 years ago after trying to fire it up in spring just to keep it in good working order it was found to be dead. Battery was replaced. The last 3 years it has always been attached to a trickle charger during the winter. This spring I went to fire it up and it was dead. Took the battery back and they did not test it, but rather replaced it with a brand new one no questions asked. The truck was immediately driven on fresh battery for an hour on the highway to get the new rims. They put them on and I drove home. Next morning I jumped in to take it to the gas station and the first crank sounded a little- just a little suspect, but it fired right up. I purchased a new Battery Tender Plus 1.5V and attached it. It flooded it for about 5 seconds and then the 80% light came on. It sat battery connected for five hours and still had not fully charged. I disconnected the battery from the vehicle and kept the trickle charger on it. It took 7 hours to fully charge.
I decided to do some trouble shooting this morning and here is what I found.

I first checked to see if the alternator was charging.

Then I check battery voltage.

Next I check the draw on the system after the vehicle had been shut off for a few minutes.

I then began pulling fuses which yielded nothing until I got to the TBC fuse- then the draw dropped.

Have I tracked this down enough to be sure I just need a new Control Module? If so, I see it's P/N 25816709. Can I just drop it in or is there something the dealership has to do to program it? Any help or guidance would be greatly appreciated.

extremity · Mar 30, 2014

The BCM has to be programmed when replaced with a J2534 pass-thru device or a Tech2. Could be dealer or any shop with these tools or capabilities.

I would first perform a visual inspection of any light bulbs, or anything staying on. Did you try pulling any of the fuses inside the truck? You have to fool the door switch to do this. But I recommend it.

68ma is is a little high. I would think about 25 or less to be normal. I have replaced quite a few body modules for drains.

n9cv · Mar 30, 2014

68 ma is a little high. GM's design point for the Colorado was less than 20 ma. At that rate the vehicle can be parked for 30 days and still start off of the battery.

My draw is 18 ma after the BCM goes to sleep.

That said, let me tell you that my erroneous draw was caused by the BCM not going to sleep. It took me several months to figure out why. The problem was a temperature / compass mirror that I added. I got the power for the mirror off of the map light. From that draw on the map light / door light circuit the BCM thought that someone was still in the truck so it stayed awake.

I'm not familiar with the abbreviation of TBC. Is that the BCM or the brake controller?

While reading the 3ma. with the fuse removed, what happens if you plug the fuse back in? Does the current go higher and then settle back down to the 60 ma. reading after a while?

extremity · Mar 30, 2014

A few more comments..

TBC is the fuse for the BCM I am almost certain. The BCM runs a lot of circuits on the truck. As n9cv stated, any aftermarket wiring changes can keep the BCM out of sleep mode.

15.07 is quite high.. 14.6 or so is ideal.. maybe the alternator is blowing out the BCM.. Have you checked AC ripple?

I really like the backlight display on that fluke. What model is it?

Parasitic Draw Help

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