The codes would indicate which sensor isn’t ready

There are no codes. Just like when I had no codes but the Catalyst monitor would not complete.

Yesterday, I drove the HHR on the highway at least 50 mph and about 60 mph for a couple minutes. The readings on the Foxwell are the same after that. I can get some pictures when I get a chance.

Taking the story at face value, The shop ripped you off. According to the report from MVA there is no indication of a bad catalytic converter, only "not ready". which does not mean "bad cat". If they had done the job correctly they would have fixed whatever is inhibiting the testing.

Here are the conditions for running the P0420 (catalytic converter efficiency) test. My guess is that it is not getting inti closed loop.
https://cimg1.ibsrv.net/gimg/www.che...2e6510e73d.png

Since he said only the o2 monitor is not ready, we presume the Catalyst monitor is ready, wouldn't that indicate that the cat (p0420 test) is fine?

This from NY.
https://cimg9.ibsrv.net/gimg/www.che...78db2b9f3a.png
https://cimg6.ibsrv.net/gimg/www.che...c4ace78a78.png

Thanks for that donbrew. I'm going to have to read that several times to comprehend all of that.

In my case, the last paragraph seems to be untrue. I had no codes, pending or set(CEL), but the Catalyst test wouldn't complete until I replaced the cat.

In OPs case, the o2 sensor monitor has not completed (2nd to last paragraph) but the Catalyst test has completed. It does say "in most cases".

A head scratcher.

I made a video while using the Foxwell NT201 on my HHR. I think either the O2 sensor is bad or the test is incomplete. Maybe I could try replacing the O2 sensor and see what happens. I got an email from the MVA January 31 about the emissions test and today (Feb 13) I got something in the mail about it.

Here's two other videos (made by someone else) on the Foxwell NT201.

Foxwell NT201 OBD2 Scanner Review-With A Color Display

Foxwell NT201 with my HHR

Ok, now which O2 sensor do you replace? There are 2 , or replace both?

I got a Haynes manual which includes the HHR 2006- 2011. I'm trying to figure that out.
I drove everyday last week, and this week I drove on the highway M-W. The HHR drives very well. If I can have work on it done at a non-CERF gas station, maybe I can take it there if it fails again. I've got two cars and one of the reasons I have the HHR is to park in front of my house next to my driveway to keep other people fronm parking there and blocking my driveway. The HHR was sitting there for about 6 months and I would run it for about 10 minutes once a week to make sure the battery stays charged. I usually drive my other car once a week and ride a bike a lot. I also live near Metro Rail (subway) and can ride my bike or walk there. Another reason I wanted a van-like vehicle is in case I decide to move to another house to get away from all the overcrowding in my neighborhood (cars parked everywhere). I should be able to move most things with the HHR.

BTW, there's videos on youtube about changing an oxygen sensor for 2006-2011 Chevy HHRs, also there's threads here on O2 sensors.