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.

Specification

Egr valve inspection
Three-way catalytic converter (twc) inspectionMazda 6 Service Manual: Dtc clearing procedure
1. Start the on-board diagnostic test mode.
2. First press the POWER button, then simultaneously press AUDIO CONT button
for 2 seconds or more.
Caution
Before clearing the DTCs, be sure to enter all of them displayed
in the on-board diagnostic test mode in the Audio Repair Order Form. ...
Mazda 6 Service Manual: Instrument cluster input/output check mode
Note
In this mode, it is possible to check the items in the following
chart.
Diagnostic Trouble Code Chart
Note
Diagnostic trouble codes which are not listed may be indicated,
but they cannot be inspected.
The diagnostic trouble codes are displayed in numerical order.
(While ...