2007 HHR 2.4L automatic trans., Started not cranking and would not crank until it sat for 2-3 minutes. When it did crank & started would run 20-30 seconds and died again. Friend with Snap-on scan tool plugged into it and read no communication with ECM when it would die. When running it would read/scan properly....................ECM going bad??? I can get a new/reman. AC Delco to replace but appears that GM still needs to "flash" unit................. Any ideas or comments on this, at a loss

 

What I think you mean is: the engine was running, you turned it off, tried to start it no starter, waited 3 minutes starter runs engine starts then immediately shuts down; now it won't turn over or start?

Ok the scanner read properly when the engine was running; what did it read? What exactly does " read no communication with ECM" mean?

Has the ignition switch recall been done? What has been done to the car recently? What is the state of the battery?

If you think there is a reason to replace computers go ahead. It would be cheaper to look for frayed wires or failed relays. Why would you think intermittent "no communication" means the computer is broken? Computers are not hamburger meat.

 

Battery checked first, checked ok. Alternator charging correctly. All recalls show done, I am the 3rd owner of this car. Car was running & communicating with scanner until it dies and error on scanner said no communication with ECM but will communicate after car sits and re-starts! I have removed connectors to ECM, cleaned & put Dielectric on everything with no improvement

 

just remind you without claiming “act like I say”
If a working engine does not start, there are only 2 reasons:
1. fuel is not supplied;
2. No electric current.
You already test electricity, pay attention also to fuel supply.
Of course, the air filter can also be guilty, but it is unlikely that the filter is filled to such a terrible state.

 

Agreed, but car starts cold and runs until operating temp. All filters have been changed previously as well as plugs & etc.. Doesn't matter what RPM the engine is when it dies like someone pulled the key out, all gauges go to the zero point as well.

 

Look into loose ground wires, and the underhood fuse box, are the upper and lower halves tight?
is there oil present around the oil pressure sender, and on the starter?

 

Is the scanner giving a code for no communication or is it not connecting to the OBD?

 

No connection at OBD when it dies. NEWEST Development...................This morning I used the key to unlock the door and it set the horn off went I opened the door! Now will not try to crank at all like the theft lock is on.................Using same keys I always have including the one I got from GM. Do I need to get the Dealer to unlock the Security on it??

 

No you need to replace the dead battery.

 

You arm the security by locking with the fob (some years by lock all on the door) you set the alarm of by unlocking the door with your key. You reset security by putting the key in the ignition. Further info is in your Owner Manual;. there is a link in my sig.