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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4906
Experience:  30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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Highlander: 2004 Highlander VSC engaged and audible alarm during

Customer Question

2004 Highlander VSC engaged and audible alarm during "normal" driving conditions.
- 2 new rear tires and old rear tires placed on front on Thrusday
- Towing ( trailer with electric brakes ) on Friday and the VSC engaged with the audible alarm while going into a turn going downhill.
- This continued to occur on a few turns here and there but not on all
- This also occurred while going uphill and coming into turns
Looking for how to narrow down the culprit between the steering angle sensor ( I think there is a TSB for this with the 04 Highlander ), the yaw sensor or something with a possibly damaged ABS component when the tires were replaced/rotated.
Submitted: 2 years ago.
Category: Toyota
Expert:  Toyota Service replied 2 years ago.
Hello. Welcome to Just Answer. Please allow me to assist you. Since you did not mention any warning lights on at the dash, experience with this exact problem would cause me to be removing the passenger side rear ABS sensor and the tone ring that the sensor "reads". Then perform a very close inspection. We have replaced several of these units (we were one of the first people to determine this issue several years ago). If the tone ring (a toothed gear that the speed sensor 'counts' is cracked, it transmists faulty RPM signals to the ABS computer. This causes the ABS to activate prematurely, and will Not set a code. The recommendation I have for you on this request is to have the passenger rear ABS components removed abd visually inspected. Replace the tone ring if found to have any cracks. Thanks for choosing Just Answer. It was a pleasure to assist you today. A positive rating for my input on this request would be greatly appreciated. Thanks again.
Customer: replied 2 years ago.
Sorry, I should have specifically stated that the audible beeping started, the VSC warning light ( the vehicle with squiggly lines behind it ) lit up and the vehicle engaged the brakes with a pulsing action ( which I would have thought to be ABS or at least analogous to the way ABS works.Also the problem has NOT occurred outside of towing on Friday and Sunday.
Expert:  Toyota Service replied 2 years ago.
This is correct. The RPM signal is most likely being compromised. When the RPM signal being sent to the computer is not matching the other three, the system activates.
Customer: replied 2 years ago.
I was under the impression though that the ABS sensor was only active while the brakes are being applied. This problem also occurred while driving uphill with no braking involved.
Expert:  Toyota Service replied 2 years ago.
The abs and the trac operate separately, but share the same rpm signal. When the brakes are applied, the abs pulses brake fluid to the wheel that has a lower or zero rpm. This would be interpreted as a skidding wheel. The trac, on the other hand, operates exactly opposite. When the rpm is 1000 on one wheel and , say 500 on the other, the trac interprets this as the 1000 rpm wheel is spinning (like on ice). The trac then applies the brakes to the 1000 rpm wheel to reduce the interpreted wheel spin condition (correct or not; it's all based on rpm)...This is done without any interaction of the brake pedal or driver input. Trac is for traction. Abs is for stopping. But the same rpm signal.
Customer: replied 2 years ago.
OK, so inspect the rear passenger ABS assembly, I assume I remove the caliper, then the rotor and then (possibly) there is some sort of cover over the end of the axle. Then I will see the magnetic sensor, the wiring and the sensor ring. I should inspect the sensor ring for cracks and clean up any residue and/or other debris and buildup. Then is there a way to "test" that it is functioning correctly?
Expert:  Toyota Service replied 2 years ago.
If you have a 4 wd highlander you will need to remove the rear axle to see the tone ring.
Customer: replied 2 years ago.
2wd with the snow assist button
Expert:  Toyota Service replied 2 years ago.
Take the vehicle to a Toyota dealer with the trailer and a comparable load. Have the attach their scan tool to the car. You drive it. Have them monitor the wheel rpm of each wheel on the scan tool. When they see an imbalance, that is where the visual inspection needs to begin.