Not sure why only one may be needed unless it relates to the difference between a AWD vs RWD, but I can tell you with certainty that when I changed my pads myself, I had to disconnect a sensor for every corner. BTW I have a 2011 AWD LWB.

I have a 2007 LWB RWD and it only had sensors on the passenger side front and passenger side rear... 2 sensors that can be bought from RockAuto for about $6 each... Total was $15 and change shipped... Look up your year and model on the site and go to brake pad sensors and you will see them listed...

Just purchased a front and back.

https://www.rockauto.com/catalog/x,c...parttype,10283

Thanks

Is the install difficult? Any instructional advice?
Can you just install them by crawling under the car?

I asked my dealer what it would take to install one of these.

$90 worth of labor?! said they had to lift the car, remove the brakes to get to where it goes.

I don't really believe him...

You have to pull the brake pads out of the caliper. So in essence your mechanic is being honest.