One problem related to gas recirculation valve (egr valve) has been reported for the 2011 Chevrolet HHR. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2011 Chevrolet HHR based on all problems reported for the 2011 HHR.
Driving along, 'low engine power' light came on (along with other errors, something about traction, something esc, engine chugging; car slows down to about 10 mph and won't accelerate; after turning car off, waiting a few minutes, car started again (but check engine light stayed on); this has actually happened to me 3 times in the past 3 weeks (I don't recall the exact dates) - I thought it might be from the extreme cold (close to 0 or below) - but today it is 31 degrees and happened again. I'm glad I wasn't on the expressway! fortunately it happened at moderate speed and I was in a place I could safely pull off the side of the road. It appears that this is happening with numerous vehicles from around that year.