Inspect for continuity between the power outside mirror switch terminals using an ohmmeter.
Mazda 6 Service Manual: Intermittent concern troubleshooting
Vibration Method
1. If malfunction occurs or becomes worse while driving on a rough road or
when engine is vibrating, perform the steps below.
Note
There are several reasons vehicle or engine vibration could cause
an electrical malfunction. Some of the things to check for are:
...
Mazda 6 Service Manual: Power Steering
Power steering is only operable when the engine is running. If the engine
is off or if the power steering system is inoperable, you can still steer, but
it requires more physical effort. If the steering feels stiffer than usual
during normal driving or the steering vibrates, consult an A ...