1. Verify that the joint shaft is not twisted or cracked.
2. Turn the joint shaft by hand and verify that the bearing rotates smoothly and freely.

Drive shaft
Joint shaft removal/installationMazda 6 Service Manual: Oil pressure switch inspection
1. Verify that the oil pressure warning light illuminates when the ignition
switch is at ON position.
2. Verify that the oil pressure warning light goes off when the engine is
started.
If the oil pressure warning light does not illuminate or remains
illuminated, inspect the related wirin ...
Mazda 6 Service Manual: Pcv valve inspection
1. Disconnect the negative battery cable.
2. Remove the intake maniforld.(see INTAKE-AIR SYSTEM REMOVAL/INSTALLATION.)
3. Remove the PCV valve.
4. Blow through the valve and verify that air flows as specified.
If not as specified, replace the PCV valve.
Specification
...