I have a 2009 Chevy cobalt ss 2.0 turbo and recently I scraped the bottom front end in a back alley and the engine light came on and lost almost all boost. Used to get 100-140kpa and now it barely goes over 40kpa. Took it to the shop and they told me it was a airflow sensor and they changed it but still not as much power.

 

you likely damaged the intercooler or a charge pipe

 

They said it could have a hole in the intercooler but they couldn't see any and I couldn't find any leaks in the charge pipe.

 

By your description on "bottom out", and not being able to build boost, you most likely cracked the intercooler like Sharkey said. It's quite common with the stock intercooler to crack an endtank, especially when hit like that. Take a good long look at it, you'll find where the hole is. It could be a charge pipe too, but one would thing the intercooler would take the brunt of an impact more than them.