I have a 2010 Chevy hhr I had a p4022 code evap small leak detected. I purchased a new gas cap in the mean time my son disconnected the battery to clear the engine light being on. What is the drive mode for the ecm to notice the catalyst and evap pending when I hook up a code reader. Any input would be great fully appreciated.

 

The EVAP tests can take 15 cold start cycles to run. I assume you mean P0422? If you disconnected the battery the pending codes should have cleared; However there shouil be no need to clear the CEL that code clears itself soon after a repair. Always turn the gas cap until it clicks 3 times.

 

Lately I get the P0422 code whenever my gas tank falls below 1/2. This has happened the last 5 fill-ups.
New GM gas cap.
I'm clueless as to the cause. I will admit, I just clear the code and move on

 

Wipe the opening of the fuel filler tube. And click the fuel cap at least three times!
Great now Tony Orlando and Dawn are singing in my head!!!