This Preliminary Information communication provides information to the technician about vehicles with misfires or roughness on cold start up. Technician may find a Diagnostic Trouble Code P0300 stored. Technician will add coolant dye to the system, run engine through warm up, pressurize the cooling system on a cold soak engine and inspect the suspect cylinder with a bore scope for coolant dye evidence. If coolant is found in the cylinder do not replace the cylinder head because that will not repair this concern. Dealer will need to contact General Motors Product Quality Center for engine replacement.
