My 2011 Chevy Hhr check engine light came on, and I cant figure out what the problem is. The Code says P0172 and says System Too Rich. Replace Fuel Rail. My brother Is a mechanic and he told me that Fuel Rails never really go out, so that's not the problem. I have REPLACED the Spark Plugs, The Air Filter, And the Fuel Pump Relay. And the O2 sensors were replaced not too long ago. So I HAVE NO CLUE WHY it is doing this. The registration just expired, and I cant get my new one for CA until i fix this and pass smog. PLEASE HELP. Any suggestions or Ideas would be much appreciated. Thanks Josh. ?????????????????
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What does the mechanic think?

First: it means the fuel TRIM is rich, which means the computer is forcing a rich condition because it is getting told there is too much air.

You might clean the MAF with MAF cleaner and the throttle body with TB cleaner. Have you ever changed the air filter? Check the clamps on the air horn. Check for air and Vac leaks.
Since you have fiddled with the fuel rail you have to suspect all of those O-rings and injectors.

Inspect:

 

I don't think he messed with the injectors, from his description. Agree, vaccum leaks, maybe the flex pipe.

 

Read possible solutions

https://www.obd-codes.com/p0172

yes that flex pipe might be the problem, inspect the fuel lines above the drivers side rear tire. See or smell gas ? Pin holes in the vapour line

 

How do you replace the fuel rail without messing with injectors?

 

Sounds like they ruled that out, since "fuel rails never really go out"

Unclear from the post, whether it was changed or not.