1. Disconnect the negative battery cable.
2. Remove the dashboard. (See DASHBOARD REMOVAL/INSTALLATION.)
3. Remove the A/C unit. (See A/C UNIT REMOVAL/INSTALLATION.)
4. Remove the blower unit.

5. Install in the reverse order of removal.
Basic system
Blower unit disassembly/assemblyMazda 6 Service Manual: Dtc c1145, c1155, c1165, c1175
Caution
When attaching the tester lead to the DSC HU/CM connector the SST
(49 G066 004) must be used.
Diagnostic procedure
...
Mazda 6 Service Manual: No.4 air intake mode does not change
When performing an asterisked (*) troubleshooting inspection, shake the
wiring harness and connectors while performing the inspection to discover
whether poor contact points are the cause of any intermittent malfunctions.
If there is a problem, check to make sure connectors, terminal ...