Emissions - Exhaust Rattle May Be Misdiagnosed As Cat
File In Section: 6 - EngineBulletin No.: 77-66-01
Date: February, 1997
INFORMATION
Subject:
Exhaust System "Rattle" may be Misdiagnosed as Catalytic Converter Rattle
Models:
1997 Chevrolet Cavalier
1997 Pontiac Sunfire
with 2.2L Engine (VIN 4 - RPO LN2)
A metallic noise or "Rattle" may be heard coming from the exhaust system in the vicinity of the catalytic converter with the engine idling while at operating temperature. The noise may be more noticeable outside the vehicle or with the vehicle running near an object that reflects sound.
A low mileage engine may interact with the exhaust system causing a rattle condition. This condition may be misdiagnosed as a catalytic converter rattle caused by a loose monolith or particles inside the catalytic converter.
This condition is caused by resonant engine vibration that exists only during engine break-in. The noise will typically go away after initial engine break-in, approximately 250 miles (400 km) of driving. Do not attempt to repair this condition by replacing exhaust system components. If the condition that is noted does not go away after approximately 250 miles (400 km) of driving, further diagnosis should be performed to correct the condition.