V1 The whole car's electrical system was dead / Now alive!

[Ross]

I was working on my BCM, looking for a ignition switched wire for my AEM Air/Fuel gauge, when I heard a click in the rear fuse box, and then the whole car was dead. No dash lights, key doesn't do anything. The BCM is clicking - some relay inside it, as removing the 2 external relays didn't stop it. To stop the clicking, I pulled the battery ground.

Checked all the fuses - nothing blown.
Anybody have suggestions?

 

[Ross]

When I turn the ignition switch, the BCM clicking stops. Not much of a clue, but accessory or run position stops the clicking.
The battery is 12.5 volts, the rear fusebox post is also 12.5 volts, as is one whole row of fuses in the rear.

 

[Briann1177]

Did you check the BCM fuses? I know you said you checked all fuses. There is a 2A fuse in the BCM that powers the ignition system. If it's not working, the it will cause things to appear to be dead.

 

[Lonny]

Make sure you have not lost a ground, this sounds like it could be a ground issue.
Wiggle all of your ground connection and see if comes back to life.

 

[Ross]

Did you check the BCM fuses? I know you said you checked all fuses. There is a 2A fuse in the BCM that powers the ignition system. If it's not working, the it will cause things to appear to be dead.

The 2A fuse is good, but there is no power getting to it.

Make sure you have not lost a ground, this sounds like it could be a ground issue.
Wiggle all of your ground connection and see if comes back to life.

I tightened the ground, and checked it with a meter, both the front and rear grounds. I don't have a center tunnel ground.

I think the BCM or PCM died. I contacted LKQ Online for replacement parts, but they only have a BCM at this time.
I wouldn't mind having extra electronics, for testing/replacement purposes... as they aren't that expensive.
I'm not sure if HP Tuners can mate a BCM serial number to a PCM... might have to get the dealer to do that. Update: No need to program a BCM... At least not in my 2006 Cobalt. Just drop in another, and you are good.
And that's if it is a BCM.
Guess I'm not going autocrossing on Saturday

 

[Ark :D]

Ross,

Sorry to hear your bad luck. If you need, you can have the BCM and ECM from my 07 SS/SC as my way of thanking you for contributing to the forum and (in the future) my build.

~Ark

 

[Ross]

This forum is better than a USA part search engine.
Thanks Ark for the parts that I can't find anywhere!

 

[Ark :D]

Ross, I am really sorry I can't come through for you on this. My first donor's computers must have gone along with the last wave of stuff one person bought from me.

 

[Ross]

No big deal. I will figure this out. It's not my daily driver, just my toy.
Awesome toy!

I am debaiting buying a stand alone ECM... HP Tuners is pretty limited on the LSJ engine.
Pros and cons anyone?

 

[Ark :D]

There is a seller on eBay that sells Cobalt ECM's that are pre-programmed to match your VIN number. The 2006 SS/SC one is $120. Here's a link to your year:

https://www.ebay.com/itm/Cobalt-SS-...-12597520-Programmed-to-your-VIN/312119821782

For others that might be interested, I am not sure if there's any difference between ECM's in the same "family" of Cobalt (ie, 2005 Cobalt SS/SC and 2006 Cobalt SS/SC), so you would want to make sure to search for your specific year.

 

[Ross]

Wow, nice find. I imagine that will save me $100 with HP Tuners, as it is licenced to my VIN number.

At this point I am learning my options.

 

[Ross]

Trying to open the BCM up to inspect the circuit board. I opened the 6 perimeter plastic clips that hold the black clam shell together... jamming 1/8" spacers as I go. But the BCM seems to be held together in the middle. Maybe those 2 metal thread inserts? Anybody opened the BCM already?

I talked to Lonny, to help me weigh my options.

First I will do more diagnosing.
I have tested the power at the 3 sources going to the BCM on the big J3 red connector. AllDataDIY refers to this as the BCM C3 connector.
D10, D12, and the main 50Amp fuse D1 all have 12.5 volts getting to them.

 

[Ross]

I drilled out the BCM two inserts past the swedged area, and inspected the motherboard. Nothing looked cooked.

I went to the auto recycler, bought an 2006 BCM out of the LT version of a car.
The dash lights up, but I'm now getting a "Power steering & Low Fuel" warnings, and HP Tuners can't communicate with the car.
The mileage is now from the new donor car... temp says 74F, coolant -40F (not reading), trip A&B are reset, as is oil life.
So I think the data isn't communicating... "GM Lan" I think it called.

 

[ccannx]

I’ve seen strange relay clicking issues with bad power supplies is there a way to check the proper voltage going to the BCM ?

 

[Lonny]

That does sounds like it could be the data wires. Check to see if you have continuity from the OBDII data wires all the way back to the ECM data wires.

 

[Ross]

That does sounds like it could be the data wires. Check to see if you have continuity from the OBDII data wires all the way back to the ECM data wires.

Okay I ohm'ed all the OBDII wires:

OBDII pin 6	tan/black strip	High speed GMLAN serial data +	Goes to Power Steering, C2, pin 1 (C2 is the grey, 6 pin connector with the small wires)
OBDII pin 14	tan	High speed GMLAN serial data -	Goes to Power Steering, C2, pin 2
Power Steering, C2, pin 4	brown/white strip	High speed GMLAN serial data +	Goes to BCM, J2, pin 1 (J2 is the white & blue vertical connector closest to the center tunnel)
Power Steering, C2, pin 5	brown	High speed GMLAN serial data -	Goes to BCM, J2, pin 19
BCM, J2, pin 2	tan/black strip	High speed GMLAN serial data +	Goes to PCM, C1, pin 1 (C1 is the blue connector on the PCM)
BCM, J2, pin 20	tan	High speed GMLAN serial data -	Goes to PCM, C1, pin 2

All the wires checked out. Put it back together, and it runs!
I'm not sure if disconnecting my AEM AFR gauge fixed it, or if reconnecting the electrical connectors made a difference. (I am guessing the latter)
I was able to hook up HP Tuners, and it was able to read data.

Thanks everybody who helped me with this. Lonny told me the BCM doesn't need to be reprogrammed, and that was great information.
It only cost me $45 for a used BCM. My new BCM was from a 2006 Cobalt with manual windows, 2.2L engine, and the old BCM was from a 2006 Cobalt SS, 2.0L SC engine, with electric windows.

I'm so HAPPY! I missed today's autocross but my car runs now :} Happy, happy, happy!

 

[Ark :D]

That's great! I am glad it worked out so well for you.

 

[Ross]

Rewired the AEM AFR gauge to get power from the BCM, C4, D4. Put the car back together and went for a test drive.
The dash went dead, and the power steering stopped assisting.
Pressed on the data connector on the power steering module, and it fixed itself.
So I have still have a loose connector that is plaguing me... at least I know where now.