I would have the car scanned to see if there are codes identifying a specific WSS fault. If you don't have a current indicator, there may be a history code. My guess is that you're onto something with a bad hub sensor. There have also been some intermittent problems with the rear wheel speed sensor wiring harness either at the wheels or where the WSS harness plugs into the main body harness. A code may give you a starting point.

Think about it. You’re tooling down the road in your Prius, knowing full-well that this thing being green is as big a sham as federally mandated ethanol-enriched gas, Russia pulling out of Ukraine, and Obamacare.

You can't see those codes with a basic scanner. It needs a more complicated scanner, like the newer Snap-Ons or the GM Dealer TechII or their new system to read. These are body codes, likely whatever scanner you have only reads powertrain codes, MAYBE ABS codes if you dropped a few bucks. The scanners needed to read this cost into the $$Thousands$$, and why most car repairs are so expensive anymore.

There are three pieces used in the stability system that require replacement when the stability system becomes inoperative and you've troubleshot it correctly. I have listed those above. In addition, the electronic brake control module (EBCM) can be a culprit too.

1) First you perform an ABS system check. If there is a fault in the ABS system, this is where the WSS comes into play. But NOT anything to do with the VSES!

2) you check that the VSES (Vehicle Stability Enhancement System) centers for roughly 30 seconds. If it doesn't, go to step 3, otherwise check all connections and wiring harnesses for intermittent connections.

3) Using your T2 (or equivalent), perform a steering wheel position sensor test. If the SWPS checks out, move on to the next step. If it doesn't, replace the SWPS.

4) Using your T2 (or equivalent), check the lateral accelerometer input voltage in the VSES. It should return about 2.5v. If it does, then the next step will be to test the yaw rate sensor. Otherwise, if it doesn't, replace the lateral accelerometer.

5) Using your T2 (or equivalent), check the yaw rate sensor. It too should return 2.5v. If it does, move on to the EBCM. If your yaw rate sensor doesn't return 2.5v, replace the yaw rate sensor.

6) Replace the EBCM. If it isn't programmed/setup properly, that could be the problem, and you'll be generating a C1248 or C1255M3 code and possible incorrect operation of the system.

No where in ANY of this, other than making sure the ABS system is funtioning correctly, is mention of the wheel speed sensor (WSS), wheel hub, etc. Why you ask?? The WSS is ONLY used for computational needs of the ABS/traction control system. NOT the Vehicle Stability Enhancement System (VSES).

I just went and looked in my Techline manual for 2004. This is EXACTLY, verbatim, from GENERAL MOTORS;

Quote:
The vehicle stability enhancement system (VSES) includes an additional level of vehicle control to the EBCM. The VSES is activated by the EBCM calculating the desired yaw rate and comparing it to the actual yaw rate input. The desired yaw rate is calculated from measured steering wheel position, vehicle speed, and lateral acceleration. The difference between the desired yaw rate and actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. If the yaw rate error becomes too large, the EBCM will attempt to correct the vehicle's yaw motion by applying differential braking to the left or right front wheel.

The VSES activations generally occur during aggressive driving, in the turns or bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the brake pedal will feel different than the ABS pedal pulsation. The brake pedal pulsates at a higher frequency during VSES activation.


Steering Wheel Position = Steering Wheel Position Sensor (SWPS) located in your steering column
Vehicle Speed = Vehicle Speed Sensor (VSS) located on your transaxle. This is NOT to be confused with your WSS out at the axles.
Lateral Acceleration = Lateral Accelerometer sensor located under the rear seat near the electrical center.
Yaw Rate = Yaw Rate Sensor located under the reat parcel shelf in the trunk.

Think about it. You’re tooling down the road in your Prius, knowing full-well that this thing being green is as big a sham as federally mandated ethanol-enriched gas, Russia pulling out of Ukraine, and Obamacare.

Have you tried a "Low Tire Pressure" reset from the main DIC? This is different than just a "reset" when the error shows up.