Completely out of the blue my passenger seat has locked itself and though it tries to unlock it is as if it's jammed. It partially opens - just a crack - and that's all, remaining locked. Has anyone else had this experience and found a solution?

 

Sounds familiar, the lock motor can wear out with time and become unable to complete a full cycle. Solution is to replace the motor, which you can get from Mazda, it's a whole assembly. Can you unlock it by hand from inside? If not, it might be more serious like a jam. You can try removing the trim around the inside door handle to get better view into the door.

 

look up door lock motors for a Mazda 6, bought two of them from Amazon $30 a piece. Mazda wanted $200 per side I think.
Also while you are doing that job, replace the big gear in the window regulator motors and a bag of the plastic door panel clips.
They break so damn easy!!
Clips
hhttps://www.amazon.com/gp/product/B09N33J94W/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1 Lock motors
ttps://www.amazon.com/gp/product/B07SWHJ9RF/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 Gears
added information

 

Thank you for that information .. much appreciated.

 

Thank you .. very helpful!

 

No problem, glad to help.

 

Oh one more thing, when you remove the door panel the puddle lamps at rear lower corners of door do not have a plug to disconnect.
You have to remove the socket from the door panel and they can and will break if you are rough.