2009 HHR SS smokes after accidental grounding of batt cable.
 

Socket fell on top of starter and when trying to remove it accidently grounded batt cable. Then started smoking quite heavily. Drove around for awhile and smoked not as much. Removed batt cables to reset ecm and smoked very little. Only in 4th gear (automatic). Drive in 3rd gear, no smoke, but when downshift to 2nd at about 1500 rpms will backfire in tailpipe. After about 2 weeks started to smoke a lot and finally got CEL and reader showed P0300. Under that it stated cylinders 2 & 4 were misfiring. Seems like ECM is no good. Can it be reflashed or does it have to be replaced? It is flashed for the GMPP kit.

What's your mileage? If it's still in warranty, I'd see a dealer about it. Otherwise, my guess is no better than anyone else's: it could well be the ECU, and you may or may not be able to reflash. I've never heard of this happening like this before, though, so I am guessing.

What do you mean by "smoke"? Exhaust, or actually smoke coming from something under the hood? Cause I don't see how this could cause the engine to start smoking out of the exhaust. That is usually oil or worse, coolant.

Definitely oil smoke from exhaust pipe. The more it smokes, the more I have to add oil. It is out of warranty. Two things can cause smoke; Lean engine, caused by misfiring or tuning too lean, or as one other member had happen--check valve stuck. The turbo is not soaked in oil, so I don't think it is the check valve. Our 496 race engine will oil if it is leaned out too far. For it to happen immediately after the socket grounded out leads me to believe circuit for injectors or spark has been damaged. Also the code that was recorded.

Went and removed batt cables again this morning and erased error code. Car is back to where it was last sat. Little smoke on surface street, but not on frwy. ??????

Been awhile since this problem. Sorry never replied. The smoke problem was the turbo. The impeller took out the backing plate of the turbo housing and the shrapnel took out the engine. So everything was replaced. Haven't done it yet, but want to put a pre-oiler in the line to turbo so it sees oil pressure before starting engine when cold. The added performance upgrades in the computer sure made a difference. Traction limited now in a big way.