G6 GT Coupe check engine light

Do a smoke test and check for a vacuum leak. Look at live data and verify that the air/fuel ratio and O2 sensors are reading properly. Also check your fuel pump for the proper pressure and flow amount.

May need to replace maf sensor ? Sometimes cleaning just will not do it.

Upstream HEGOS are one of the main active signals to the computer which controls the air fuel mixture. Scan it again write down the code(s) "lean" is to basic. Don't change any parts until you scan again.

Did it shut if instantly or did you have to drive it a bit before it went off? If it was off immediately, he cleared the code and it came back on when you put 40-50 miles on it. You should have to drive it 40 or 50 miles before the check engine light goes off to know that it's fixed. I had that same code on the Yukon I had, ended up being an intake gasket leak

Make sure your radiator is completely full of coolant, and that your overflow box is completely full too. If you have a intake gasket leak, it will idle kinda rough until it pushes that extra antifreeze out. Then whenever it's not so pressure rise with all the antifreeze from losing some it'll start running normal again. If you try this and it works just how I said, then it's your intake manifold gasket. Like I said, I had the exact same code on another vehicle, and it wasn't even the mass airflow sensor. And ended up being an intake manifold gasket leak or shot the same code