One problem related to manifold/header/muffler/tail pipe has been reported for the 2008 Chevrolet HHR. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Chevrolet HHR based on all problems reported for the 2008 HHR.
Exhaust fumes coming into cabin when heater is turned on. Caused by faulty, cracked flex joint on downpipe, connected to exhaust manifold. Have to ride with windows cracked for fresh air. Gm refused to repair. Stated outside 80,000 mile emissions warranty. Car has 82,419 miles.