I bought my 2009 HHR SS in Jan 2026. I did not pass emmissions with no codes. The inspectors ask if I cleared codes. (i did not) The ecu was not ready. I did get a code a few days later for low coolant temp. I changed the thermostat and checked out the o2 sensors and found I had only 1 o2 sensor and it was before the cat. and no sensor behind the cat (the hole was capped). I traced the wire and found the connection on the driver side behind the tire attached to the block. I believe that connection was for the down stream o2 sensor. The problem is I do not see the connection for the up stream o2 sensor in the harness..
How am I not getting a code for the missing o2 sensor? Where would the other o2 connection be?

 

You probably have a "tune". Ant stickers under the hood or at the fuel filler? I suspect that the cat has been "cored".

 

X2 what^^^he said. You need to get the down stream sensor installed and connected, possibly need to replace the catalytic converter if it was cored!

 

Did the inspector state exactly why it didn’t pass?

 

I got the idea it was "not ready".

 

Nope it’s not !

 

The emmission was not ready . After talking to a few people I found the up stream o2 up on the manifold, ( looks like I have and oil leak ) the down stream o2 sensor was installed before the cat and the hole on the cat that the down stream o2 goes into was plugged. I have to move the o2 .

When I drove the car the engine coolant temp was only 163 , I replaced the thermostat now the coolant reads 193. On my scanner the up steam o2 goes in to closed loop and the down stream does not go into closed loop So the down stream o2 needs to be moved to the back of the cat so I can pass NJ . emmissions.

 

Correct!

 

Whoever you are talking to about the O2 sensors is wrong. The #1 sensor controls the A/F, the #2 sensor monitors the health of the cat. They are different parts with different jobs.
The fact that the emissions is "not ready" means that not all of the OBD2 tests have not passed. My guess is that since there is no #2 sensor the cat test will never run. My bet is that the car came from an area that did not have emissions testing and I bet the cat has been cored (innard removed) and I bet the ECM has been tuned.
Please ignore all advice you see on Facebook.

 

And if you clear the codes or disconnect the battery or the ECM, the readiness testing has to start all over again.