Slip indicator light at 55mph

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Racer5112, Mar 24, 2019.

  1. Racer5112

    Racer5112 New Member

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    Hey guys!
    I have a 2007 Prius that the slip indicator light comes on when I'm going about 55-60mph and goes off when I let off the throttle. All the tires are the same size. No 'beep' happens, just the light. I just replaced the TPMS in the front right wheel. Worst part is, I had to replace it before I drove the car for the first time, so I don't know if it was doing it before the TPMS was replaced. I've tried doing a bunch of reading about this, but can't really find anything specific to my problem. Any thoughts?

    Thanks,
    Mike
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    What is the tire inflation pressure on all four tires?
     
  3. Racer5112

    Racer5112 New Member

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    35 on all 4 tires.
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    OK, do you find that the tread depth is similar on all four tires? The issue is that the skid control ECU thinks one tire is rotating at a different speed vs. the other three.
     
  5. Racer5112

    Racer5112 New Member

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    They are all pretty close. Is the ECU really THAT picky as well? Yikes...

    I'm trying to sell this car, but I don't really like the idea of trying to sell it if this light keeps someone from going down the interstate since it won't go over 60mph it seems like.
     
  6. fuzzy1

    fuzzy1 Senior Member

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    Are they also the same brand and model? If not, do they at least have the same RPM (revolutions per mile) on their spec sheets?
     
  7. ChapmanF

    ChapmanF Senior Member

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    If you have Techstream, you can have somebody watch the four wheel speed readings while you're driving to see if there's one that looks off.

    There's also a special wheel sensor test mode you can select, which is more sensitive than normal driving, and will tell you about sensor problems after just a low-speed jaunt around a parking lot. That's standard procedure in the manual for after any work on the sensors, to make sure there's no issue before returning the car, but it doesn't always seem to get done.
     
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  8. Racer5112

    Racer5112 New Member

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    Ok, I'm raising my hand to be the first to tell me that I'm an idiot... question is, does the ECU really get that picky?

    I was able to look again at the car yesterday and found that the front tires are 185/65/15 and the rears are 195/55/15. There is an inch difference in overall diameter between the two. I want to sell the car, but want to be sure if this is the problem. I'm willing to do a different set of tires on the front, but it is hard for me to believe that the ECU is that stubborn on having to have the perfect size tire on the car..
     
  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The four tires must be the SAME size, which is not the same as saying they must be a perfect size. In your case, the rear tires are incorrect.
     
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  10. Skibob

    Skibob Senior Member

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    If your going to sell the car get 4 tires that are the same size. Cheap new tires always looks better than mismatched tires.

    To the folks that asked, the ECU is not that picky. I have 1 tire that has 28,000 miles less than the other 3 (road hazard replacement) and I have no problem. They are all the same make, model and size though.

    BTW, how did you not know there are 2 different sizes of tires on the car? Did you just buy it or something?
     
    #10 Skibob, Mar 26, 2019
    Last edited: Mar 26, 2019
  11. davecook89t

    davecook89t Active Member

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    Exactly the same thing happened to me a couple of weeks ago with our Gen 2. The 2 front tires were worn, so I wanted to replace them. Our car is the Touring model, so it is supposed to take 195/55/16 tires and that's what the tire store (Tires Plus in Fort Myers, FL, affiliated with Firestone, I believe) put on. I asked the manager to move the tires that were on the rear to the front, if he thought that was necessary. I was willing to pay for that. I was not willing, however, to pay for the engine and cabin air filters that he tried to sell me for what I thought were exorbitant prices. Anyway, he put the new tires on the front and left the old rear ones as they were. I then allowed him to talk me into having a wheel alignment done, which I did not think was entirely necessary (I was not experiencing any steering problems or unusual tire wear, but he had a print-out showing that the toe was pointing slightly inward on both front wheels).

    When I got in the car to drive off, I noticed that the HV battery monitor was showing only one purple bar, which I thought was most unusual, having rarely seen it at that level before. Since it was a warm day and I was going to be sitting in traffic with the A/C running all the way home, I force-charged the battery up to a more reasonable level before I left the parking lot. When I got the car up to speed (right around 55 mph), I noticed the VSC light beginning to flicker. At first I didn't think too much of it, possibly the new tires had a slightly larger diameter than the old ones and needed to be worn down a bit, but we were planning to drive back to NY the next day, and I didn't want to be worrying about that issue the whole way, so I took the car onto the highway and brought it up to 75 or 80 for a few miles to see if the light would go away. It did not. The VSC light turned on steady at 55 to 60 mph and would not go off unless I reduced speed. After a few miles of this, I happened to glance over at the MFD and almost $hit my pants when I saw the battery level again at 1 purple bar. At that point, I realized the HV battery was not being charged with the VSC system disabled, and I knew I would have to go back to the tire store. I was convinced they had screwed something up, but I checked all 4 tires just to be sure they were the same size, and wouldn't you know it, the ones on the back were 205/55/16. In the end, I was forced to buy 2 more new tires for the car. I now have 4 new tires, costing more than $500, on our 2007 Prius with 274k miles on the odometer.:eek: I was initially reluctant to buy even 2 new tires, with that many miles on the car.

    My question is: how is it possible that the VSC system didn't give me a problem until I put on the new tires? I replaced the front tires at Pep Boys shortly after I bought the car at around 211k, and I'm pretty sure they put the correct tires on the car. The problem, I believe, arose a short time later when I had the rear tires replaced by our local mechanic (who is a friend of the family but has been known to cut corners, at least when it comes giving out state inspection stickers. One time, he gave me a new inspection sticker for my 1995 Toyota Hilux Pickup, and a couple of months later told me I needed new rotors, because the worn out brake pads had scored them.) He apparently put the wrong size tires on the car (I'm assuming he didn't want to lose the business by telling me he didn't have the correct ones), but somehow adjusted the alignment so it would not trigger a VSC code. Is that even possible?:unsure:
     
  12. Skibob

    Skibob Senior Member

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    Look at the size differences here
    TireSize.com - Compare Tire Sizes, Specs, Prices & more

    The circumference of the 205s is 78.1”
    The circumference of the 195’s is 76.8”
    So yes the computer sees the tires moving at 2 different speeds and the 1.3” difference is enough to trip the computer.

    I guess the 28,000 mile difference with my 1 tire is within spec. They are all the same size, make and model.
     
    #12 Skibob, Mar 26, 2019
    Last edited: Mar 26, 2019
  13. ChapmanF

    ChapmanF Senior Member

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    Why the tire size difference causes the VSC light is clear.

    As to a connection between the VSC light from wheel speed sensors and charging, I'm skeptical. Sounds more like coinkydink to me.

    Some problems with brake control, if detected by the brake/skid ECU, will disable regen braking, but not all possible problems; I wouldn't think wheel-speed mismatches necessarily qualify. And disabling regen braking doesn't mean the battery never charges; the engine will run extra to charge it.

    There is a known connection in the other direction: if the HV or battery ECU thinks the battery capacity is impaired, they will send word to the brake/skid ECU to lay off the regen braking.
     
  14. Skibob

    Skibob Senior Member

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    The OP’s tires work out even worse.
    185/65/15 is 76.8”
    195/55/15 is 73.6”
    That’s 3.2” different
    Gonna have to change 2 of them.
    Fronts are OEM
    Rears might work all around or you could get tires rubbing on something in the front. Don’t know myself.
    4 new cheap matching tires look good on a car for sale.
    $40.97 - Westlake RP18 185/65R-15 tires | Buy Westlake RP18 tires at SimpleTire
    40.97 each and free shipping
     
    #14 Skibob, Mar 26, 2019
    Last edited: Mar 26, 2019
  15. davecook89t

    davecook89t Active Member

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    Thanks for adding to my knowledge of the way the system works. I was surprised to see the battery discharge like that and wanted to warn the OP that might happen. So, our car was not necessarily exhibiting typical behaviour, then? The funny thing is my wife was with me in the car when I took it out on the highway and both of us had forgotten to bring our phones. If I hadn't happened to glance at the MFD, we could well have been stranded on I75 between Exits 143 and 158, probably the only section of that road with such a long distance between exits. We are now back in New York and have had no problems whatsoever with the car after putting on 2 more new tires.
     
    #15 davecook89t, Mar 26, 2019
    Last edited: Mar 26, 2019
  16. Skibob

    Skibob Senior Member

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    4 new tires at 274k. You’ll probably run them to the wear bars and need a new set. ;)
     
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