If our 2011 Equinox was equipped with a new muffler, a technician would run an engine check and find that the intake and exhaust camshaft position solenoid was defective. My mechanic said this is a common problem with GM 4L engines. I saw one person on You Tube uninstall and install both. So I just did the same thing, after 20 minutes the engine died and the car was working as it should. Not sure what they are doing but GM should call back if this is an issue.