This Preliminary Information communication provides information to the technician about vehicles that may have a engine noise is sometimes louder than expected. Also will explain the known normal and abnormal reasons why the engine may be louder. When the vehicle speed is between 25-50 miles per hour the road noise does not mask the engine noise this is considered normal. When the vehicle is first started for the day the system will perform a catalyst preconditioning for about a minute. At this time the engine will seem louder than normal, this is normal. At times the engine often runs at wide open throttle, but at a reduced speed. This sound is uncharacteristic of a four-cylinder engine in a traditional sedan, but is a characteristic of an extended range electric vehicle such as the Chevrolet Volt. Technician will be able to inspect for abnormal induction ground-out conditions. These locations should be checked lower rubber isolator on air box not installed correctly or missing, upper induction resonator cover not installed properly, refrigerant line not bolted to engine support bracket, and throttle body contacting coolant pipes behind it. Abnormal exhaust ground-out conditions should also be inspected. These locations are at the exhaust clamp rearward of the second catalytic converter is contacting the battery heat shield, exhaust resonator underbody is contacting the heat shield. Repair any abnormal issue found.
