GM Duramax: "Service Emissions System" but no DTCs??

Got called in to a shop 2 hours away to look at a 2012 GMC Duramax Diesel that is stuck in LIMP MODE due to an Emissions System fault. Shop owner already replaced some parts, and no DTCs are set! The messages displayed are: “EXHAUST FLUID QUALITY POOR” and “SERVICE EMISSIONS SYSTEM”. How do we […]