I did read a lot of threads on the subject but I have the code and my HHR is running fine. Any idea what I should be looking for, 2008 LT with 198,000 miles

 

The throttle body connections can be simply dirty and corrosion has set in. Check the connection for loose or bent pins. Clean and dielectric grease the connections.
Do not move the butterfly plate manually, clean it with CRC throttle body cleaner.

https://www.obd-codes.com/p0121

 

I have been looking, found nothing yet. Have to continue looking. I find it odd that it's running so good with no drop in mpg after reading other posts on the subject. Thanks

 

It might just be the harness was pulled at during an oil filter change. Just enough to trigger the OBD II code.

 

Have you tried clearing the code to see if it returns ? Since you don't see anything obviously wrong and you say it's running fine, maybe it was just a false, fluke reading.

 

Great point FMG, perhaps a battery lobotomy will clear this up. It will clear the codes. If it comes back , then you can go from there.

 

Agree with that and see what happens. (or doesn't )

It could be that simple. Or it will be diagnosed the last place you look, possibly...

 

I have cleared the code a number of times and it comes back. Something odd today, started out this morning no check engine light, stopped at the drug store came out started the car engine light on, went to Walmart came out no light. Didn't come on after that.

 

That indicates to me a loose wire either in the harness connection or a ground wire.

 

Just a update on what's going on with my check engine light. After disconnecting my battery on number of times the light would go out for maybe three or four days. I then unhook the battery and unplugged every electrical connection under the hood that I could access. I cleaned all connections use Dielectric grease plugged everything back in reconnected the battery and now the check engine light will stay off for about a month at a time. Again I will unhook the battery the light goes out I can get a another month with no check engine light. I'm not sure what to try next.