I believe the speed sensors would be the Driver's Side rear. The wires sometimes get frayed or the sensor itself gets clogged with a lot of dirt and road grime. The sensor is located behind the wheel hub assembly.

To get at it, remove the wheel and look behind the Brake Dust Sheild - you should be able to trace the sensor cable to it's location. You will see a Black Plastic box in your wheel arch that houses the sensor's connector. Check in that first and clean it out. Then check that the wires are not pinched or frayed and exposed.

After that, remove the sensor from the mount (you'll need Allen Wrenches to do this) and clean out that hole. You can spray WD40 in there to clean it or similar. If you have compressed air - that helps.

Re-install and see how that goes. You may still need to order a new sensor, but try checking it out first.

The below diagram should give you an idea of where it is. It is Item #23.

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