Ok, I have never done this before and I’m hard headed, so someone throw something heavy and blunt at me if I am making a mistake.

We hooked up the Nano and the laptop, set the car to “run” by holding the bottom of the start button down for 5 seconds (you know when it switches from Accessory to Run), then started Tech2Win, navigated through the Model, product line, and transmission questions for the computer diagnostic option, and it kicked out those codes.

The kid found a list of the error codes for an 05 C6 online, and I wrote down what they mean, and for one of the codes, a faulty BCM was listed as a suspect.

I assume error codes with a B at the start have to do with anything powered, like B as in Battery, since they all have something to do with circuits, relays, and voltages, correct?

The U codes are all lost communication codes with various modules, possibly because those modules don’t wake up until ignition? Or they require communication with the BCM?

Should we start with the B error codes?

Do we need to do the scan while the car is cranked and running?

— codes located at http://www.c6registry.com/technical/ls205codes.htm

 

Start with the U codes, since you have problems on both the High speed lan bus, as well as the class 2 bus as well.

As for B codes, voltage from battery goes to engine fuse box, then to BCM, then out to modules in the car.
So check battery first to make sure it's at least 13.2 volts, then BCM voltage to make sure it it at least 13 volts, then the problem modules to make sure they are at least 13 volts as well.

Also, when you go to start the car with a dead battery, going to get a lot of codes popping up due to the modules glitching from low voltage then. So on that note, clear all the codes, then start the car a few times with fully charged battery, to see what codes are popping back up.

 

Sir:

Battery is less than two months old, has never died, stays hooked up to the battery tender, and registered 13.7 volts right before I ran the scan.

I know that the current is good at the under hood fuse box, and that there is 13V going into the BCM. I checked every wire between the two with both a tone generator and the multimeter. I also know that the drain remains when I unhook everything from the BCM, but leave it plugged in, so I know that it is getting power because it isn’t going to sleep.

Where/how do we check the voltage going out of the BCM? At each pin on the connectors?

I am out of town for work tonight, but I will clear the DTC error codes tomorrow evening and scan it again.

 

I use the tech II on all the modules to pull up their data up, which will include working voltage at the rest of the modules.

As stated, battery should be at least 13.2v (14.5 if motor is running), BCM at least 13v (13.2~.8 if motor is running), then down line modules like ECM and RCDLR that are powered by the BCM fuses, very close to 13 volts for them as well. Hence at most, should only have .02 drop in voltage from the BCM voltage, due to the adding wiring voltage drop, from the BCM to them.

 

It's a known issuse and one of several reasons I sold my 05 mn6.

Do a forum search for DBS (Dead Battery Syndrome) and start reading.

 

So, I was dealing with that same problem in my 2005 C6. I replaced the fuse box with a new one, transmission module for a new one. The way I found out and correct what it was, at least in my case, My car was starting slow and one day it just did not started. I went and purchase a new battery, that was not the problem, I called the mechanic and he told me to purchase a new starter as the corvette ones suffer from the pole loosening and making a false contact, you will not see it until you remove the starter. That was done almost a year now, problem solved, so far no more battery draining, he placed the tester and there was no drain. I also installed a starter insulator, as he told me that in this corvettes it was too close to the header and it was causing that on the long run due to the heat. In my case, this fixed my battery drain.

Hope this helps.

 

FYI, but you can replace the starter solenoid on the starter ($20 for the solenoid), isntead of having to replace the entire starter at hundreds of dollars instead.

But yes, since the battery cable to alternator wire connection point is at the starter solenoid lug, it's nut loose can cause charging problem to being with.

 

Thanks for the heads up! I did read that this was a problem, hence the reason we disconnected the starter from the battery in the OP. There was no drain on the battery when nothing was hooked up to it, and no drain on the battery when only the starter and solenoid were connected to the power, so I’m fairly certain the parasitic drain isn’t coming from a short in the starter. The drain is bad enough that you can watch the voltage on the battery drop when the battery tender isn’t hooked up, and I was unable to recreate that drain when it was just the starter and solenoid attached to the battery terminals.

The drain is 100% certain coming from the BCM not going to sleep, I’ve got that established. The question is “why not?”.

 

That was what we originally assumed was wrong with it. Testing has yet to produce a result that makes us think it’s something different.

 

Ok, we used the Nano to run the diagnostic scan on the car today. The boy was at work, so the girl got to play gopher for me.




The first thing we did was clear the DTCs from the ECM.




Then we went for an hour long drive, and baby girl got her first lesson on how to drive a manual transmission. Fun times.

Came home and parked the car, but left it running, and then ran the diagnostic scan again. Got the following list of codes:




So we tried to recreate the codes by clearing the DTCs again, turning off the car, cranking it, and driving for another half hour.

Left it running when we got back home, hooked up the Nano, scanned it, and it remained DTC free.




We then checked every possible option along the tech tree on Tech2Win. We found no DTCs on any module, and everything looked ok voltage wise at the various modules we looked using the snapshot option.

So we turned the car off again, fired it up, let it run for a couple of minutes, checked for DTCs (none), then turned the car off and repeated it.

No DTCs being generated across three start/stop cycles, including a half hour of highway driving.

Repeat: The car is not posting new DTCs.

Is there anything else we need to check, or can we finally assume the BCM is the culprit?

 

Forgot to add pics of the scan results when we called it quits:

 

I'm fortunate to live in the Denver area, and when I first bought my 2007, Dan invited me over and he taught me so much --in just one day-- about inspecting, maintaining and repairing problems. Especially with the electrical system, but also induction, brakes and suspension.

Thanks Dan!

I'm reading this amazing thread because I have a Courtesy Light in my Review Mirror that won't shut off. But I feel small, with this tiny problem, compared to what I have read here. (Although this can and has killed the battery for me.)

edit: Well, I messed with the buttons today, and I must have done something right. The light is off now. But I still plan to always use the battery Tender on it. Same as my little airplane needs.

 

Hopefully someone else will find this useful in the future, though I have no clue how. It has required like 75-100 hours of us just standing around poking at the car with probes and wires. 😜

 

Always hated the knee bolster button, since it a stabby a kind of thing and wait to see if its correctly.
GM would have been off with a button that locked inwards, release outwards, so at least you know that you had it the wrong position when you stabbed it with your knee and the mirror lights stayed on/did not dim out..

 

Put the BCM in to sleep mode via Tech2win, and see if you still have the higher battery amperage draw problem.

If yes with BCM in sleep mode, then not hard to pull the BCM board out of the case to see if you have a corrosion problem across some traces/header pins that is causing the draw problem on its own with the BCM in sleep mode.

Also, check the car for either a XM module, or GM pal in the car (will be in the same location), and make sure to unplug it for the battery draw test. There was a firmware update flash for the C6 that causes all kind of problems with both of them not going into sleep mode on command from the BCM.


http://www.kawal.net/PAL%20rev2%20install.htm

Next, would check for a I simple device behind the radio, since they have been known not to go into sleep mode on command from the BCM if they are still searching for a Blue tooth device to connect to.

Last one, Would look long and hard for any GPS tracking device wired into the car that may have been installed at some point, since they can get power hunger as they start to burn out and again, will be pulling power from the BCM, since it powering everything inside the car.

If you need to replace the BCM, PM or Email me and I can hook you up with TIS2000 to SPS firmware flash the new BCM into the car. With this being a 05, there are couple of firmware update flashes you may want to do as well (RCDLR being one of them) that may not have been done, and may be what is holding the BCM from not going into sleep mode to begin with as well.

Also, with stock disc radio in the car, it may not have been update flashed, and can send you are CD to update its firmware as well. The original main problem was a static problem that the firmware update resolved, but update flash did a few other things as well.

 

Yes, sir! Will do! I appreciate the offer, and I will keep updating. Thank you!

Edit: Do you know what I need to press to put the BCM into Sleep Mode?

 

Disconnected the XM receiver, as suggested.



Did not see a PAL.

Hooked up the DMM and let it sit for 20 minutes.




And that cut the DMM’s reading for the drain in half. It was showing 70 mA with XM receiver connected when the car was supposed to be asleep, and it’s showing 30 mA with it disconnected. Kind of. It will show .03 for five or six seconds, then it will bounce between .03 and .04 for about two seconds, then settle back to .03 for five seconds.

Both are still half of the drain that it was showing, though.

The internet says 25-30 mA is acceptable drain for a new car, does this count as “new”, or do we need to keep searching for more possible drains?

Edit: We can leave the XM Receiver unplugged, can’t we? We don’t use XM.

 

Ok, that did not stop the battery drain.

After three hours of no drop in battery voltage, I took the car out for an hour long cruise with the XM Tuner unhooked. When I returned home at 5 PM, I turned the car off (It is in reverse), gave it twenty minutes, and then checked the battery voltage. 12.94 V. Checked it again twenty minutes after that, and got 12.82.

So did a voltage drop test, and the DMM read 20 mA for the draw. Gave it twenty more minutes, still reading 20 mA.

So I hooked the battery cable back up to the terminal and measured voltage. 12.74 V.

As of now, (8:10 PM) the battery is reading 12.62 V.

At this rate, it will be below 12 V in 10-12 hours.

I have no clue how that is happening with a 20 mA draw.

Edit: I am going to hook up the DMM again and see if the mA drain has changed. I will update it again before bed.

 

If you are not using XM, then pull the module. As for selling it, it's a double edge sword since it may not be firmware upgraded yet (that only the dealer can send in to do), may be firmware screws up from the other flash that did not allow it to go into sleep mode, and would still have to be cleared to allow it to marry to another as well ($50 from a third party).

Drain wise, your in the normal range now (car should be good for a few weeks off a tender sitting, if battery is still good), so good to go unless you want me to point out a few more module that can be disconnected as well.
Hence your really not using the VCIM (unless you total out the car in a wreck and your insurances want to pull it's data), so its connectors can be pulled, and just have to jump out the tan wires on the two connectors so you don't break the GM land bus circuit. On the 05, the VCIM in the front side of the rear passenger back chubby behind the carpet. Next would be On star, since it another one that draws power when the car is suposed to be in sleep mode.

Also, would take a good look in the engine bay, pull the front driver bottom valance, and even the radio so get a good look in theses areas for a GPS tracking device. They are easy to spot, since they will have wires off them that are tied into the factory wiring, but the wiring will not look like it factory from the start. Hence excess wiring, with Zip ties/double sided tape holding such in place.
Note, if GPS tracker is found, and you are making payments on the car, get a hold of your loan company to make sure they are not the one that installed it. If you do pull one they have installed by them before you pay the car off, they will come repo the car at your expense, will install another one, which you get to pay for as well, before you get the car back, even if you are current on payments.

As for battery, would do a quick check on the charging system and alternator, and even charge the battery and have it load tested.
Fully charged battery should be in the 13.2v range for AGM, and even higher to wet cell, so something is off with either charging system or battery to start with.

 

Showing the 20 mA draw. This is the second time I’ve gotten this draw in a row, and the previous test was 30ish mA, so I agree, I think the electrical system is ok.

But the battery is still going down. I’m waiting the 20 minutes for the car to go back to sleep after I hooked the battery cables up, I’ll post pics of the voltage over time, before bed.