Traction control light comes on-slows car down to 20 MPH, Fix?

It would seem to me maybe you need to at least check both of the front wheel sensor wiring making sure they're all plugged up clean I think if you use an ohmmeter and you pick up the given side and turn the wheel You should be able to count the beats on your multimeter according to the amount of cut outs passed by the sensor . Or something similar to that seems to me the car is being told to put that on the traction control that is because it's not seeing something which is why you don't have a code. Or it's really seeing something and activating traction control completely and doesn't need to I've never seen that happen on one of these every time I see traction control I'm losing traction and can feel it right underneath my car with me in it so for it to be activating and nothing going on sounds like some sensor is not being sensed or not even plugged up or in the mix at all.

 

If you don't have it, try to get TechStream, You can monitor each wheel speed sensor to see what they are showing for detected MPH.
It may not be the one you think.

 

Get Techstream or one of the capable scantools in this thread.
https://priuschat.com/index.php?posts/3290690

Several can access ABS system data to view wheel speed sensors.

Might be one tire might have different size. Might be cracked tone ring on the LF axle. Sometimes the WSS mount is off some (corrosion under sensor or damaged screw)- but usually that causes "false" ABS activation on braking.

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I am pretty sure the skid ECU has a "check mode" that the repair manual suggests using after hubs have been changed and so on. In the check mode, you drive around a little bit in a certain pattern, and the ECU looks at all of its sensor signals and holds them to a much stricter standard than it normally does, so it's very likely to flag any issues that might be missed or intermittent in normal operation, and if the whole check mode routine passes, that's a pretty good indication of health.

At least, I know Gen 1 had such a check mode and Gen 3 does, so I'm guessing Gen 2 does also, but I don't have that repair manual in front of me at the moment.

 

It'll be in the Repair Manual:

Toyota Service Information and Where To Find It | PriusChat

In the Gen 3 manual, for example, the heading is really SENSOR CHECK USING TEST MODE, and can be entered with a jumper from TS to ground, and it starts the brake warning lights blinking, and then you do nothing for a second, then stomp the brake for 3 seconds, then drive over 28 MPH for several seconds till a light goes out, then stop till a light blinks, then drive in a U turn at about 3 MPH, then stop and park, and a buzzer sounds for 3 seconds if everything went right. You will then have tested all the wheel speed sensors, the acceleration sensor, the master cylinder pressure sensor, and the yaw rate sensor.

But the procedure in my old Gen 1 was different, and I'm sure the details are different in Gen 2 also. As you can see, you kind of need to be looking in the right repair manual for your model to know the right sequence of things.

 

Did you ever resolve this? I'm having almost the same issue. Dealership isn't seeing any codes, all the wheel speed sensors have been checked, one even replaced. Still happens that I slow down to 15mph and it won't accelerate again until I restart the car.

 

You can view the repair manual in PDF form online and lots of places that has nothing to do with here so for copyright problems and all that whatever the case may be. Some of the guys here will point you to a link that either they know of or what have you The three manual set for this car can be bought on eBay original Toyota product for around 250 bucks yeah it is a stretch for some but there's nothing like having the real paper manual set for a car that you're trying to keep for well almost ever It's actually cheap insurance if you want to look at it that way some of the processes in the manual are 30 pages long and longer It's quite a lot to try and text to people on the fly in a post and then you have to sit down and really read it and be able to look at it while doing it and so on some of it can be very lengthy and a lot of elimination is going on so you need to be able to keep track of it. So it is a great thing to have if you're all in on the vehicle it's like a no-brainer and people who have aged out gotten out of these cars whatever are getting rid of this stuff You can buy real nice copies on eBay while they're still around real ones I'm not talking about the PDF copies and the fake printed copies of the real manual The real one I think they're blue they're three volumes when you put them all three together they're hard to pick up.

 

Any update to this issue? I had a wrecked car. Drove fine with a bent control arm. Changed control arm and aligned it. Drove fine. Had some hub noise. Replaced them. While jacked up on stands I noticed the driver axle was wobbly so replaced it. Drive side control arm bushings don’t look great. But everything was driving fine badly aligned after the wreck. Now after replacing the hubs and everything I have this issue and can’t figure it out.

 

You have to find the repair manual then online and you've got a lot of reading to do. Three posts above or so Chapman f describes the basic business but when you work on these cars regularly all this stuff kind of runs together it's hard to remember the procedure for each series of vehicle but you've got some tests that you need to run to see what's going on. All the tires on the vehicle are the same size?

 

I think I got it figured out. I made sure alignment was ok. Then in techstream there was a skid control code. Cleared it but it didn’t fix it. I went ahead and reset the brake memory. Did a relearn of the yaw. Then linear valve relearn. And it’s good. Alignment was off way worse after crash and it didn’t have the issue. So not sure what happened but it’s fine now.

 

I'll go out on a limb and guess that your problem was the steering angle sensor or the yaw sensor not being "reset".

The ecu sees data from one sensor that the car is turning, but the other says it's not turning - so the ecu is programmed to cut power back (and apply braking on one corner?) to prevent a crash from severe oversteer or understeer.

I have read that stability control can get very unhappy if it thinks that the car isn't "going straight" down the road when it actually is.

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She'll go crazy, gas, no, brake, right, no, left, gas, no, brake...))