DTC A1 Front Sensor Bus Communication Error: DTC Detecting Condition

WARNING: This page is about a different car, the 2013 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.

Harness between airbag control module and front sub sensor is open or shorted.
Front sub sensor is faulty.
Airbag control module is faulty.

CAUTION:

Before diagnosing the airbag system, be sure to turn the ignition switch to OFF, disconnect the ground cable from battery, and wait 60 seconds or more before starting to work.
When replacing the airbag module, seat belt pretensioner, roll connector, control module and sensor, reconnect each part and check that the warning light operates properly.
When inspecting the airbag main harness, disconnect the airbag module connectors and seat belt pretensioner connectors of the driver's and passenger's seats for safety reasons.