Check for an exhaust leak in front of the converter, check that the O2 sensors on that bank are OK as well. A slow or contaminated sensor can toss a false code. Check the fuel trims as well. Just to rule out something other than the cat. If those are OK then replace the cat. I wouldn't do both unless they are a welded assembly. Haven't looked at an HHR in a while so I don't recall the exhaust configuration.
Sunday, March 26th, 2017 AT 1:07 PM