Do you know a GMC Service technician?

[DouginUtah]

A couple of months ago I bought a truck in a private sale.

2006 GMC 2500HD, 2WD, 6.0, 4-Speed Automatic, VIN 1GTHC24U8 6E150047

The seller failed to inform me that the truck had an electrical problem. Rip-off number one.

If I allow the truck to sit unused for a few days the battery is drained. I thought maybe just a worn out battery and almost bought a new one. But I gave it a full charge and disconnected it for a week. Connected it back up and it still had a full charge. So, not the battery.

I take the truck to my non-dealership mechanic. We pull all the fuses and relays and it still is draining. He talks to his friend at the dealership and they decide it is the Body Control Module (BCM).

I did a Google search for "gmc body control module" and got 3,640,000 results. Apparently this is a major GM problem which I had never heard about.

My mechanic said $600 for the BMC and $100 to have the dealer flash it with the right program.

I went to a different dealership and explained my situation. He said they might be able to flash the existing BMC with an updated program but I would have to have the service tech look at it.

Of course, the dealership could flash it and say, Nope, it didn't work so we had to put in a new BMC. Not that a dealer would ever do that!     $565.00 profit at the price quoted to me. It is this second rip-off I am trying to avoid.

My question for a service tech buddy would be: Do you know if there is an updated program which the existing BMC can be flashed with to correct the problem?

My mechanic is looking for a used BMC--there are dozens for sale on eBay for $100-$125--but he is not on the internet, and I don't know if buying one off eBay would be advisable, since I would have to get it flashed by the dealer.

I am not aware of anyone here who is associated with a GM dealership. If you are, or know someone to ask I would sure appreciate some help in getting this resolved.

Hope you can see my dilemma. What would you do?

[Warbird]

What would I do?  Not let the truck sit for a few days without either running it or disconnecting the battery.  Unless there is some other problem this deal is causing...?

[JohnG28]

Sorry I cant help you with your dealer issue, but do you know what the BCM is and does?  I get that with all the fuses/relays removed that there are no open circuits, but that doesnt diagnose an issue before the fuse panel.  Also, are there any aftermarket accessories? They may not have been wired through the fuse panel.  Maybe have a look at the main cables running from positive terninal of battery, anything frayed? Just some suggestions, hope they help.  Id definately check all possibile places before replacing something that spendy.

[Ianab]

Or one of those big Battery Isolators connected into the main lead from the battery. If you aren't going to use it the next day, flick the switch?

Ian

[Captain]

ANY aftermarket accessories inappropriately wired into the vehicle, my favorite is a LoJack, can cause the BCM to stay in high power mode.   

Captain

[DouginUtah]

The only addition/modification done is a 6-pin trailer light hookup. No LoJack. No security system. Low end factory radio (although it does sound too good to be factory!?)

To add to what I have said...
We disconnected the alternator as I was told that a failed diode could cause a drain. I had the alternator checked at Autozone and it checked out good--diodes okay.

[Reddog]

Have you had the battery load tested? A bad battery can read over 12 volts.
You could have a cell going bad.
I always like to start with the cheap and simple.

[DouginUtah]

We are sure it is not a battery going bad. We have used a ??? light which shows there is "significant" current draw with ignition turned off. Okay, the light doesn't show "significant" draw but when connecting the cable to the battery there is a considerable spark. The light does show that current is flowing with the ignition off.

I just wish I knew whether the existing BCM can be flashed and be brought back to spec--sort of like rebooting a computer when it gets hung up.

[easymoney]

could be an alternator going bad. disconnect the wires going to the alternator and see if you still have the spark when you disconnect the battery.

[DanG]

Get a helper and find a really quiet spot.  Take one battery terminal loose, then touch it back to the post, listening for any little clicks in the vehicle.  If you hear anything at all, have the helper crawl over, under, around and through the vehicle while you continue touching the post intermittently.  Last time I did this with the same problem, we found it to be the ABS relay on the rear brakes.

[Brad_bb]

Yeah, the juice has got to be bleeding off somewhere in the form of heat or work.  Find it. I'm sure there is a better forum for people who have dealt with this.  I often go to chevytalk.com.   Go to the correct year truck section and ask your question.  There's a guy with user name "Chevytech" who is very knowledgeable and has helped me with several issues on my truck.

[Captain]

Significant arcing when reconnecting a battery is normal. 

A light bulb check on a disconnected battery for parasitic draw is not sufficient, further a draw test switch that keeps continutity to the battery is essential.  When the battery is disconnected, a component that is causing the draw may not be re-activated (such as a relay, etc.)  The vehicle stays in "high power mode" for a period of up to 45 minutes before reaching its normal sustained parasitic draw of under about 22 mA.

There is no calibration for eliminating parasitic draw from the BCM in the GM system for 06 MY.

Captain

[Captain]

Disconnect the battery negative cable. Refer to Battery Negative Cable Disconnection and Connection .
Install the male end of the J 38758 to the battery ground terminal.
Turn the J 38758 test switch to the OFF position.
Install the battery negative cable to the female end of the J 38758 .
Turn the J 38758 test switch to the ON position.
Road test the vehicle and activate ALL of the accessories, including the radio and air conditioning. This may take up to 30 minutes.
Important: Leaving the key in the ignition on some vehicles may cause a parasitic drain that is above the recommended amount. Refer to Body Control System Description and Operation .

Park the vehicle. Turn the ignition switch to the OFF position and remove the ignition switch key.
Connect a 10-amp fused jumper wire to the test switch tool terminals.
Turn the J 38758 test switch to the OFF position. The current now flows through the jumper wire.
Wait one minute. If the fuse blows, install an inductive ammeter to locate the current draw.
Turn the test switch to ON and then remove the fused jumper wire.
Set a digital multimeter to the 10 A scale.
Connect the digital multimeter to the test switch tool terminals.
Turn the J 38758 test switch to the OFF position. The current flows now through the digital multimeter.
Wait one minute. Check and record the current reading.
15.1.  When there is a current reading on 2 A or less, turn the J 38758 test switch to the ON position. The electrical current will now pass through the switch. 

15.2.  Then switch the digital multimeter down to the 2 A scale for a more accurate reading when the J 38758 test switch is turned OFF.

Turn the J 38758 test switch to the OFF position. Wait 15 minutes for most vehicles.
Check and record the current reading.
Note the battery Reserve Capacity, amp hour rating. Refer to Battery Usage .
18.1.  Divide the reserve capacity by 4, amp hour rating by 2.4. 

18.2.  Compare this to the multimeter milliamp reading taken in the previous step. The parasitic current drain should not exceed this number. Example: If a battery has a reserve capacity of 100 minutes, (60 A/H) the current drain should not exceed 25 mA.

If excessive current drain is not found at this time and there are no other apparent causes, complete the following:
19.1.  Using the MIN/MAX function of the digital multimeter, monitor the parasitic drain overnight or during the day. This will determine if something has been activated during that time frame.


         Notice: The test switch must be in the ON position when removing the fuses in order to maintain continuity in the electrical system. This avoids damaging the digital multimeter due to accidental overloading, such as a door being opened to change a fuse. 



         Important: Removing fuses, relays, and connectors to determine the failure area may wake up modules. You must wait for these modules to go to sleep or use the sleep function on the scan tool. 


19.2.  When the vehicle has an unacceptable amount of parasitic current drain, remove each fuse one at a time until the current drain falls to an acceptable level. This will indicate which circuit is causing the drain. Refer to Power Distribution Schematics to diagnose exactly which part of the suspect circuit is causing the parasitic drain. In some cases a non-fused circuit or component, such as a relay, is the cause of excessive parasitic current drain. 

19.3.  Repeat the parasitic current drain test procedure after any repair has been completed to make sure that the parasitic current drain is at an acceptable level. 

19.4.  When the cause of the excessive current drain has been located and repaired, remove the J 38758 .

Connect the battery negative cable to the battery negative terminal.

[Captain]

I don't know where your prices are coming from, but the list price on the BCM is $308 (part only)

Programming the BCM is a 3 step process that requires the vehicle be present.
1) BCM is programmed with GM software.
2) BCM is configured for truck options with a scan tool.
3) Theft Deterrent system is relearned to accept new BCM, or truck will not start.

Captain

[DouginUtah]

3) Theft Deterrent system is relearned to accept new BCM, or truck will not start.
Captain

Okay, I admit I am in this way over my head. It is obvious that I will have to have the GM service tech fix this.
If you would just clarify one point...
You state 'new' BCM. Are you saying I have to buy a new BCM or can the existing BCM be reprogrammed, and is it likely that the problem is just a defective BCM?

Thanks for your replies Captain. Your help is greatly appreciated.

-Doug

[Captain]

Actually, I doubt the BCM is the source of the problem.  It is actually a pretty routine diagnosis to find a constant parasitic draw for a service technician.  You should be able to isolate the source rather quickly with the above mentioned diagnostic.

There is no GM issued "corrective software" for a BCM that may be causing a parasitic draw.  The old BCM is, however, reprogammable.

Captain

[JohnG28]

You mention a 6-pin trailer hook up was added.  Have you used it or checked its condition?  I had a Jeep with with a 6-pin hook up, the points had corroded and shorted out, which caused my battery to die a couple times until I found the issue.  Might be a place to check.

[DouginUtah]

I want to thank everyone who has offered help. The problem has been solved--at least I am lead to believe so, although sitting for week will be the definitive test.

This has sure been a learning situation for me as far as being open-minded enough to accept ideas that I am 'sure' are not relevant.

Have to go. More later.