Subaru legacy 11 feels like I’ve backed into something

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I reversed and my car went about a foot then felt and sounded like I hit something, I got out checked I didn’t. I drove straight reversed again and it did it again. Today it is fine reverses fine but any idea of what this could be?

 

[Ecmbuster]

2011 Subaru Legacy < Requires the correct identification and engine version.

Automatic Transmission 5EAT
Subaru Legacy 3.6L 5AT 4WD R Limited Sedan 2010, 2011, 2012, 2013, 2014
Subaru Legacy 3.6L 5AT 4WD R Limited Sedan w/EyeSight 2012, 2013, 2014
Subaru Legacy 3.6L 5AT 4WD R Premium Sedan 2010, 2011, 2012, 2013, 2014
Subaru Legacy 3.6L 5AT 4WD R Sedan 2010, 2011, 2012, 2013, 2014

These transmissions have problems with "speed sensors" and torque converter "slip".

Hard gear engagement can be caused by a one or more speed sensors. The transmission control module will react to one or more speed sensor errors.

The entire vehicle network requires a scan to determine the origin of the fault.

At least, check the transmission fluid level and have the model scanned.