Used techstream to investigate the xmas tree on the dashboard of our 2014 RX350. After clearing codes the ones that were consistent had to do with the left and right speed sensors. I did a drive with techstream and observed that in fact the two rear speed sensors were zero the entire time, while the front showed the correct MPH. Is this a coincidence of both sensors failing or does anyone have suggestions of anything else to look at?

Thanks in advance!

 

That is an odd one and leads me to suspect another cause for the issue rather than the speed sensors themselves. Was there other recent work done on the car or a recent accident etc.?
Have you inspected the wiring harness to them?

A Google search lead to this Toyota 4 Runner forum thread on the same issue and they suspected either the wiring or the Skid Sensor. I had not heard of a Skid Sensor but apparently it is related to the ABS module or may be the ABS module etc.
You may need a more experienced independent Toyota specialist to conduct further diagnostics before throwing random parts at it. I doubt replacing both rear speed sensors would work and they are difficult to replace on the RX as I think it is the entire hub assembly.
​​​​​​https://www.toyota-4runner.org/4th-g...d-sensors.html

 

The rear wheel speed sensors on the FWD RX350 models are indeed built into the hub assembly (which in my eyes is a design flaw). Fortunately, the front wheel speed sensors are individually replaceable.

 

We took it to a Lexus dealer and they said that rodents chewed threw the harness that carries the rear speed sensors. I'm a little confused only because I inspected under the rear of the car the day before and traced the speed sensors from the wheels to the first connection point, and then from there in to a central harness that seemed to go up in to the bottom of the trunk space. It seems odd to me that only the two rear speed sensors would be affected.

I'm not an expert, but my worry is what they saw cut was actually a hitch harness as our RX350 came with the tow package. I saw 3-4 cut wires under the rear but they we dangling from the master harness, and given we have no tow hitch connector I assumed that was what it was. Anyone smarter than me know better. Does the OEM tow package really not include a power harness like I assume?

 

It appears you were probably mistaken in identifying those wires. The techs probably ran additional tests to identify the broken wires.
You did not state if the dealer repaired or replaced the harness and resolved your problem. What was the cost estimate or final cost?

I have confidence that the dealer techs are skilled and familiar enough with the wiring on the RX to differentiate the hitch wiring from the speed sensor wiring.
Although it has been years since I installed the hitch, I recall the hitch wiring on my RX was tucked away and hidden under the plastic cover under the rear of the vehicle on the driver side.

 

I will let you know - they had to order the harnesses so TBD :-)