Subaru made a design change made to the rear ABS wheel speed sensor on 2015-2018 Legacy and Outback models. In order to better protect the sensor harness from road debris, an additional shielding cover was installed.
PART P/N APPLICATION
RIGHT REAR SENSOR ASSEMBLY..........27540AL10B.............2015 Outback
27540AL12B............2015-2018 Outback
27540AL08B............2015-2018 Legacy
LEFT REAR SENSOR ASSEMBLY.......... 27540AL11B............2015 Outback
27540AL13B............2015-2018 Outback
27540AL09B............2015-2018 Legacy