I was emailed some tips that helped me find an issue. HHR is running again. No backfeeding parasitic draws. It does still stay running for 5 seconds after key is removed. Only code is in the BCM U2105-00. Body/theft deterrent lost communication with Engine Control System.

If that means anything to any, please advise me

All the research Google provides with this code seem to be a no crank/start issue. I am the opposite in a way, I can crank and start but cannot shut off.

 

Communication loss U2015, check the ECM connections any loose pins of ground wires.

 

I don't know where you got the "Body/theft deterrent" part of the description, that is not included in the GM book. I means that the GMLAN is broken at the ECM. Why is the result of the double secret troubleshooting a secret?
My guess at the over running is a bad switch or the wiring. When they did the recall they seem to let the lot boys do the work on many of them. We have had many reports of sloppy work. Something is keeping the drive train relay energized; maybe a bad relay.

In this case the ECM:

 

The scanner I use (OTC Evolve) decoded the code as Body control/ theft deterrent circuit had lost communication with ECM.

The code is not setting an MIL I had to specifically scan the BCM to see it.

It can be removed with key on engine off, but returns after engine is started.

I do not know if it loses communication during running time or if it occurs during the 5 seconds after key is removed until ignition actually shuts it down. I will check that tomorrow.maybe that will help diagnosis.

I will follow the steps provided above to test the harness and module. Thanks for the info.

When the engine is running, all live data is normal. I plan on driving it tomorrow and recording data. I will perform the above test 1st in hopes of a smoking gun.

 

One more thing I can add is I replaced the ignition/starter switch on steering colomn because it only worked if pressure was applied to it. Anyway, on all other Cobalt, Ions, HHRs, etc that I have ever replaced thus switch on, a security relearn was needed before it would crank again. This time, it simply fired right up. That and the scanner claiming issue with theft deterrent makes me curious.

 

If you didn't replace the PK3 module you don't need a relearn.
There is a long very involved chapter about the Power Mode system and the GMLAN. There are fail safes in the system that will prevent the engine from shutting down under certain circumstances.. The modules are constantly exchanging signals.

 

Is there a way to test yje PK3 module? Also, the PK3 module "slides" up and down colomn exposed. Is that normal and only in fixed position with cover reinstalled?

 

I don't know, I think the module snaps on. The book is too confusing on the subject. In one place it says the PK3 module is only an exciter and the cylinder does the handshake stuff; in another the module does it all; in some places it says it only affects the fuel continue; some places the BCM does everything in others the ECM is involved.

Anyway, if the engine runs and the security light is not flashing the PK3 is working. A flashing light means tamper, a solid light means malfunction.

 

Thanks again for your opinion. I agree it seems to be working properly as I can start the vehicle, I have no solid or flashing security light, or any MIL. However the delay on ignition kill is puzzling. If the delay is truly the only symptom, I may have a daunting task to find culprit.

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Spend $2 and replace the run relay. They sometimes do stick; I spent a couple hundred dollars on my home AC before I thought to look at the $5 "contactor" that what AC guys call the compressor relay.