Fuel Systems: Emission Control: Emissions procedures
Checking & cleaning a PCV valve
 
Most modern vehicles have a PCV valve, which should be checked periodically to make sure that it is not clogged with deposits from the exhaust waste.
 
Obtaining & interpreting scan tool data The standard procedure for diagnosing an OBD II vehicle is different as it requires that the codes should NOT be cleared until the vehicle is repaired.