Left rear sensor needs replaced?

Had a similar problem with a 2007 RAV4.
In the end for me, it was the CABLE that connects to the sensor - might be worth a look-see (otherwise, for the RAV4, the only option was to replace the entire wheel hub assembly (with integrated speed sensor)).

Taking a quick look, it appears the Gen 3 Prius is the same for the rears - sensor is embedded (experts please chime in if incorrect):
https://www.rockauto.com/en/moreinfo.php?pk=3183438&cc=1444360&jsn=549&jsn=549

 

Yeah could just be the cable connection to the sensor, which is embedded in the rear wheel bearing. It's very difficult to disconnect, and if you've ever had work done the locking mechanism may be partially broken. I would check that first, just in case the shop hasn't. You can access without raising the car, just crawl under and look at the rear of the wheel connection to rear axle: there's a single cable going in: make sure it's on and pushed fully in.

FWIW on ours are the rear speed sensor connectors are "compromised" on both sides, but I've just made sure they're fully pushed in, and they've stayed that way.

If it is the sensor, that is built into the rear wheel bearing, and will necessitate replacement of the bearing. $600 for that seems a little steep.

The Toyota bearing sells retail online for around $230 (plus shipping, maybe $30~?):

Rear Axle for 2010 Toyota Prius | Toyota Parts

Part number: 42450-47040

For me in Canada, nobody in the States seems willing to ship to Canad. So plugging the above part number in at Amayama (Japanese online retailer), I could get it for $183 CDN. That's full price, with shipping. I've used them 3 times now, and have incurred no extra taxes or duty. Delivery is a little slow, typically around 2 weeks, but they have been 100% reliable for me so far:

Genuine Genuine Toyota 42450-47040 (4245047040) HUB & BEARING ASSY, REAR AXLE for Toyota Prius - Amayama

Screen-grab, from my locale:



That $183 CDN converts to around $137 US. Full price, genuine Toyota part, delivered to your doorstep...

Rock Auto, the big US automotive retailer, sells a variety of bearings. I believe Timken is respected, might even be Toyota's source? Maybe around $150, plus shipping.

The install, is maybe an hour. There is a DIY technique, using threaded rods with nuts and washers, to slowly pry the bearing off. For pros, experienced, I can't see it being more than an hour.