Slip indicator light when going about 60mph

I would think that mis-match might very well cause the problem you describe, I bet the ABS monitoring computer is getting confused with the apparent different speeds at which the wheels are spinning, and thinks "Ah, slippage! DANGER! Will Robinson! ICE! That's what it has to be!" Of course if the control software had been tested more thoroughly, this would have been seen as a possible scenario in QA, and the tyre size (…and thus speed) would have been factored into the software!

 

I'm at a loss for an explanation, but all I can say is The ChuggyPig is shod with identical Michelin Energy Savers on the original 16" rims for the warm part of the year, and I've just ordered a set of 4 Blizzaks to be put on the 15" steel rims for the snow season, and the only time I've noticed the "DANGER, Wil Davis! There is slippage in the traction sytem!!!" light, is occasionally when I've been on black-ice, or on painted lines or metal man-hole covers on the road! (You just get used to it!)

 

It could be due to the sensor, maybe it's just more sensitive to speed changes than the others. I believe aftermarket sensors are pretty inexpensive, if you want to see if installing another one has hopefully, a better outcome.

 

The Gen 3 Prius has a wheel sensor on each wheel. I assume the Gen 2 is the same. Even my 17 year old truck has 3 sensors (1 on each front wheel and 1 on the rear axle.)

You should have 4 tires of the same size for the ABS to work correctly.

 

The 2008 Prius does have 4 wheels sensors. Here is a parts catalog showing all four parts:

08 2008 Toyota Prius ABS Speed Sensor - Brake - Beck Arnley, Standard Motor Products, Front Left, Front Right, Rear Left, Rear Right - PartsGeek

 

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Yer lucky it's just a sensor going off, once had to while changing wheels on a gen 2, (the tech broke a bead) run two different sizes front and rear, at 30 mph the ice died, it would run at 29 fine, ignore that particular mechanic that advises different sizes front and rear

 

OP, I'd go further and say ditch that "mechanic" and find a new one.

 

Though the same size tires should be used, it's a little lop sided running the donut spare. I don't remember off hand the maximum speed with the spare tire.

 

Isn't it marked on the side-wall?

 

Yes it is. I just didn't want to walk outside to my car and take a look. It's probably about 45 mph. Wild guess.

 

don't blame the mechanic unless he suggested running mismatched tires. there is no good reason to run different sized tires on a prius. they will turn at different speeds, and as you've seen the traction control won't like it.

 

There is no problem using using either size providing all 4 tyres are the same size. It is worth noting however that 205/55/16 will give a more accurate speedo reading, and are also surprisingly considerably cheaper to buy.
The OEM 195/55/16 size gives a speedo reading about 3% faster than actual speed. Tyre dia 24.4 inches
The 205/50/16 will give a reading about 4.6% faster than actual speed. Tyre dia 24.1 inches
The 205/55/16 will give a reading about 1% faster than actual speed. Tyre dia 24.9 inches

Calculation for tyre dia is:- Tyre width (205mm), x aspect ratio (55%), convert to inches divide by, (25.4) to give sidewall height, x (2) number of sidewalls in the diameter, + (16) the wheel size.
Alternative use one of the many online calculators.
Tyre sizes vary slightly by manufacture, and by the amount of ware.

John

 

This happened to me after I reset my ABS/VSC System with my tech stream. Same tires as I’ve always had since I got it. It’s only as I approach 60mph, the light starts flashing and it acts as though I’m loosing power, like it would when the traction control kicks in when the front wheels start to spin? Weird.

 

You can use Techstream to look up the reasons for the most recent four (I think it's four) times the traction control was triggered. It will have the vehicle speed, g forces, speeds of all four wheels, etc. That will probably bring you very close to a conclusion on what's going on.

When you say you "reset" your "ABS/VSC System" with Techstream, what did you do exactly? And was there a reason you did that?

 

Try ChapmanF 's suggestion to see what data you can get to figure a diagnostic direction. Top of the list is something funny with a wheel speed sensor. While that could be a sensor itself is glitching, it could also be that the front and rear sensors are reporting slightly different speeds, and the difference between those speeds is great enough at 60 that it triggers the traction control.

So if the event data record suggests that wheel speeds triggered T/C, you might want to look at tire condition, and try rotating them front to back. Yes, they are the same tires that you have had for awhile, but if the fronts have been on the front the whole time then they could have worn down more than the rears to the point that it's just past the T/C trigger threshold at higher speed. Not super likely (if all the tires are the same brand and size), but possible.

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