Ok. You checked the fuses. You checked the pin switches in the door for power. All appears ok. Next you have to remove the rear side panel to get a look at the arm from inside.

The first pic is the extender unit minus the seat belt loop(on left).
Second pic shows the likely break point which is the gear on the right. It's plastic. Do you hear the extender motor running continuously? Try this test. Car off. Ignition key on. Open and shut door. Motor should cycle if the break point gears are broken and not jammed.
The blue wire is attached to the pressure switch. If this gear is not broken is could be jammed with debris. The pressure switch is attached by two screws. Some times these screws loosen up and these small switches can not function.
The third pic shows the componants removed from the support bar. Following the long black cord around almost to the end you see four small chrome like screws. These screws secure two position sensors. These too may loosen out of alignment and the unit ceases to function.
Worst case scenario the unit's brain has failed. That's the black box to the right of the first picture.

Attached Thumbnails

     

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