Solman 98 did your hhr went to engine Pwr Reduced state?
What was the symptom on that code for you?
Thank you

 

Soloman98 did your Hhr went to Engine Pwr Reduced? Mine go in that state every time the check engine light appear.
What was the symptom on yours with the code 121? Did you get the 2135 code too?

 

P0121 is the probable culprit. My own 2007 HHR LS 2.2 got several "engine power reduced" warnings back when it was new. There was a mismatch between the voltages produced by the throttle position sensor and the sensor in the accelerator pedal. It was caused by a bad connection (a loose or broken pin) inside one of the major plugs in the wiring harness. The dealer located the defective connection and fixed it. My HHR has not thrown a single code in the past 7 years.

 

Kornellred thanks. It was the same description in mine.
Finally I fixed the problem. I use a lot my HHR on freeway for traveling and abuse use of the cruise control. Too much acceleration and deacceleration. So the potentiometer used to regulate the throttle opening, has a internal malfunction at some point. I changed the TB AND THE CODES vanished after 4 minutes running w/the new throttle body. I took me like 20 minutes to complete the process.
Thanks everybody 👍

 

Glad it's repaired, enjoy that HHR!

 

Cleaning the throttle body as suggested twice already, may resolve your problem.