Traction Control On When Switching from Reverse to Drive?

First thing to come to my mind is a faulty wheel speed (Hall) sensor. Perhaps it could also be corrosion in the wire harness connectors. To start off, I would check all of those connectors and make sure that the wheel reluctors are not covered in rust and dirt. Clean everything up and go from there.

 

Nitpicky point, maybe, but Hall effect sensors are only one, rather specialized, kind of magnetic field sensor, that can be used for certain magical things like making current clamps than can measure DC. I think there are some in a Prius (in the accelerator pedal and the shift selector, at least), but I don't think the wheel speed sensors (or the crank, cam, or MG1/2 resolver sensors) actually use the Hall effect.

-Chap

 

Do you have any ABS Codes?

 

Could be a bad steering angle sensor. You will need to have Toyota check for codes that may have been picked up by the computer.

 

Are you sure that you have come to a full stop before shifting from reverse to drive?

 

Pressing on the brake pedal too hard while at a stop can trigger this. Sounds like the answer. Try not mashing so hard on the brake after the car has come to a stop.

 

Here’s what you do to prevent your light from coming on.

 

I haven't dealt with the ABS/wheel speed sensors on either of my Prii, but unless they're different than other cars, they are indeed Hall Effect Sensors.
HES's are also commonly used as Crank Position Sensors for timing purposes in internal combustion engines.

 

This video may be a good place to look.

A visual inspection is always a good place to start.

 

The Toyota manuals are pretty explicit about identifying which sensing technology is used for each application in the car. For example, the 2004 (Gen 2) New Car Features manual covers the use of Hall sensors in the shift position sensor (page CH-13), the shift control actuator (CH-16), and the accelerator position sensor (TH-38). The MG1/2 resolver sensors use a simpler technology (ordinary coils, one fed by an AC signal, the other two picking it up off the oval rotor; page TH-29). The cam and crank sensors are plain pick-up coil type (page EG-19). The steering torque sensor with its coils is described on CH-78.

The wheel speed sensors don't seem to be detailed in the New Car Features manual (maybe they weren't a new enough feature?) ... but for Gen 1 anyway, they can be seen in a clear diagram on page DI-366 of the 2001 repair manual. Plain pickup coils again, showing the sinusoidal waveform you'd expect, and a simple resistance test between the two coil terminals.

It's clear why they would use Hall sensors for the accelerator pedal and shift selector; after all, those sensors have to accurately read the position of a magnet, even when the position isn't changing, and for that you need the Hall effect. The other applications like wheel speed and crank position all have a toothed disc happily spinning away in a magnetic field, and nothing would stop you using Hall sensors for that if you just had them lying around, but you certainly don't have to, as a plain coil and permanent magnet can do that job.

-Chap

 

Doggone it Chap, I'm not even done with my first cup of coffee this morning and you've made me go and learn something!

My knowledge of Hall Effect Sensors is limited exclusively to automotive/motorcycle applications -- used to sense position of the engine for timing and fueling purposes, and to sense the position and speed of wheels for ABS.

Your post made me Google "Hall Effect" which led me to Wikipedia and a fascinating read on Hall Effect Theory.

It seems the use of Hall Effect in the automotive world is about the simplest use of the theory -- a bianary, "yes or no" to determine the position and/or speed of a rotating object. I had no idea about the more sophisticated applications.

I'm going to take the rest of the day off. This thinking business is hard work!!

 

My 2011 (prius II) 128K had the traction control come on during driving on steady roads no bumps, a few times a week, every now and then. I had the original factory 2011 battery back then.

After I changed the 12v battery the issue seemed to go away but it did happen one or two times in a year now.

I wounder if my old 12v battery would go down in voltage and trigger my traction control for some unknown reason.

I never continued to troubleshoot this since it's almost all gone with the new battery.

I just assumed since it was electrical, the new battery helped put all the sensors and electronic devices back to where they should run at.

If you still have that old OEM 12v battery a new one could help.
my2cents.

 

I think I needed to learn something too. Gen 1 and Gen 2 manuals show speed sensor waveforms that are sinusoidal and get closer together and taller with increasing wheel speed, as you'd expect for simple passive magnetic sensors.

In the Gen 3 manual, the waveform illustrations have changed, to square pulses that get closer with speed but have constant height, because starting in Gen 3 they really are using some kind of active sensor like Hall effect. And this thread's in the Gen 3 forum, so that was right all along, and it was my bad for taking the thread on a detour. Live and learn.