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The great speed sensor mystery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by dragonrand, Apr 19, 2014.

  1. dragonrand

    dragonrand Junior Member

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    2005 Prius with package VI and 245k miles on it. I drive about 500 miles/week because I don't live close to my office.

    I've decided to only buy Toyota wheel bearing/hub assemblies from now on. I had both front hub assemblies replaced about 15 months ago, and one failed within about 9 months (driver's side). The shop I use was great and they replaced it under warranty at no charge. Last weekend I had my tires rotated, and imagine my surprise when Firestone said (and showed me) that my driver's side wheel bearing was again completely worn out. They begged me to immediately stop driving it, rent a car, and have my car towed back to the original shop for another warranty replacement. (I didn't - I drove it the 50 miles there.)

    Back at the original shop, I prevailed upon them not to do another swap for the same part, but to return the failed part to their parts supplier and instead order this 3rd replacement hub assembly from Toyota, which they did. There was a small cost difference but since it'd only been 6 months since the last warranty replacement they obligingly ate the difference. But before they could send me on my way, they informed me of another problem, which is the true topic of this thread.

    During their post-work test drive, my VSC and ABS lights came on, and their code testing indicated a bad front left speed sensor. They ordered a replacement from their usual (non-Toyota) supplier, which they said would be roughly $70. When it actually arrived, it was not the correct part, and they then determined that the correct part was actually in the ballpark of $250, regardless of whether I went aftermarket or sourced from Toyota.

    So my first question is: Does that seem like a reasonable price? I've looked for any discussions of the speed sensors in these forums, but they don't seem to turn up much.

    As I've driven the car in the day since I got it back I've noticed several things, all new (wasn't doing it before the hub assembly replacement):
    1. Mileage has gone done down by 5-7 mpg.
    2. The VSC/ABS dash lights seem to reset themselves every couple of times I take the car out.
    3. Braking force is indeed inconsistent and the VSC (swervy car light) does come on regularly as if the car does indeed think my wheel(s) are sliding, although they're not.
    4. Cruise control at city speeds (30-50mph) is also "surgey". It's as if the car doesn't know how fast it's actually going so it constantly makes under- and over-corrections. I didn't notice that on the highway drive back.
    5. Have to drive more to confirm, but it seems that when the trouble lights are on, the car realizes something is wrong and therefore disables VSC. Braking seems consistent when the lights are on. This may also be why I didn't notice problems with cruise control being erratic on the highway drive home? The lights were still on then.
    Now for the codes reported by the code reader I borrowed from a nearby parts shop. There are a dozen of them.
    • C0205 - ABS Current Left front wheel speed sensor signal malfunction
    • C0371 - ABS Current Yaw rate sensor output signal malfunction
    • C1236 - ABS Current Metal stick to speed sensor (FL)
    • C1271 - ABS Current Low output voltage of right front speed sensor
    • C1272 - ABS Current Low output voltage of left front speed sensor
    • C1273 - ABS Current Low output voltage of right rear speed sensor
    • C1274 - ABS Current Low output voltage of left rear speed sensor
    • C1275 - ABS Current Abnormal change in output voltage of right front speed sensor
    • C1276 - ABS Current Abnormal change in output voltage of left front speed sensor
    • C1277 - ABS Current Abnormal change in output voltage of right rear speed sensor
    • C1278 - ABS Current Abnormal change in output voltage of left rear speed sensor
    • C1281 - ABS Current Master cylinder pressure sensor output signal is faulty
    Now the follow-up questions.
    1. Would a single failed (or failing) speed sensor screw up the system voltages enough to cause it to throw all those other codes?
    2. Would a speed sensor be most likely to cause this or one of the other sensors in the ABS/VSC system?
    3. Is it likely that they disturbed the left front speed sensor while replacing the hub assembly? I don't believe in coincidences most of the time, though they do happen.
    4. Could I clean or repair the sensor somehow? The shop said it's just a coil with a magnet on it - seems pretty simple, and pretty steep at $250 if that's the typical price.
    Incidentally, I've never replaced the 12V battery. I know a weak battery can cause all kinds of weirdness and I can't believe the battery is still good, but I've tested it periodically over the past couple of years, and again just this afternoon. It still seems rock solid: Diagnostic mode reports about 12.3V in accessory, 11.9-12.0V powered on (but not running), and 13.8-14.0V when running.)

    I apologize for a long thread, and thanks in advance for all replies!

    Bryan
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Most of the DTC you listed are not valid Prius DTC. C0205 and C1236 are valid. The first means that there is a problem with the LF sensor while the second means that there is contamination at the tip of the LF sensor. So it would be reasonable for you to raise up the LF corner of the car, remove the tire, remove the sensor, and see if it would help to clean it. Use brake parts cleaner spray. If you don't have that, isopropyl alcohol would be OK.

    2. It is certainly possible that the sensor was damaged or dropped during the hub replacement process, you'll have to take a good look at it to see if you can detect any physical damage. Also look at the rotor teeth to make sure none are chipped or damaged as that could be the cause of C1236.

    3. You can buy the correct sensor for $171 plus shipping here. MSRP is $228:
    2005 Toyota Prius Parts - AutoNation Toyota Gulf Freeway Parts

    4. If you are willing to install a used part, try autobeyours.com to determine availability and pricing.

    5. The 12V battery is on the marginal side, since you measured 11.9-12.0V during IG-ON. It should have provided a pretty long service life since you log so much READY time per week.
     
  3. dragonrand

    dragonrand Junior Member

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    Patrick,

    Thanks for the clear advice. I'm willing to remove the sensor for inspection/cleaning, and if necessary, replace it myself with a new one. Thanks for the links to buy parts.

    Where exactly do I find the sensor? It is fairly straightforward to locate and remove/inspect? Been searching for images or videos of this but without much luck, so I'm not sure what I'm looking for.
     
  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    When you raise up that corner of the car and remove the tire, then it will become pretty obvious where the sensor is. You will see the sensor wire cable running from the wheel well interior, then attached to, and running down the strut. Follow that cable down to the end, and you will see the sensor attached to the steering knuckle/axle hub assembly. Tightening torque of the screw that holds the sensor is 71 in.-lb.

    Do not confuse the sensor wire cable with the hydraulic brake line which is connected to the disc caliper. The former is flexible while most of the latter is rigid steel tubing, with a short run of flexible rubber tubing which allows the suspension to move up and down.
     
  5. KhaPhoRa

    KhaPhoRa Member

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    Also when they reassembled they may not have seated the dust shield correctly. There is a hole in it and it needs to line up with the hole for the speed sensor so it can properly detect the ABS exciter ring. It could very easily just be a little debris on the sensor tip though. When I swapped out my wheel bearing hubs one small fleck of metal stuck to the tip and triggered all my vsc abs lights as well. If you take it out and it's definitely clean try to safely look inside the hole to see if you can see the exciter ring. Also inspect the exciter ring as if it was damaged it too could cause your issues. Might as well check those before throwing money at a new sensor (it's really not that delicate of a thing). The picture is of a generic exciter ring so you know what to look for. All those teeth are detected by the sensor as the wheel spins so a single chipped tooth could confuse the system. [​IMG]


    the Seahawks training facility ?
     
  6. dragonrand

    dragonrand Junior Member

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    Thanks Patrick. I snapped photos of what I think is the sensor.

    IMG_2922.jpg IMG_2923.jpg IMG_2924.jpg IMG_2925.jpg




    If that's it, it certainly looks munged up to me. If I'm understanding the pic you sent along with what I see when I look at where the sensor seats, I can imagine how a piece of debris (or if it were possible to attach the sensor too close to the exciter ring, the ring itself) could tear up the tip of the sensor. Is this pretty clear visual evidence that the sensor is damaged and needs replacement?
     
  7. KhaPhoRa

    KhaPhoRa Member

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    That's the sensor and yes it's definitely damaged.. It can't physically get too close to the ring; fully seated it will sit a small distance away. Either something was stuck to it when they put it back in or it was damaged when they had it out. If you don't think they'll replace it for free you might as well clean it up as best as possible and see if you can't center that post a little bit.. It might work while you wait for a replacement. Definitely check the ring for damaged teeth as well at this point.


    the Seahawks training facility ?
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Probably. I suggest you compare to the sensor on the RF wheel to be sure.
     
  9. dragonrand

    dragonrand Junior Member

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    Thanks KaPhoRa and Patrick.

    I could've tried cleaning it up, but it looked so obviously damaged to me that I just stuck it back in. The car's back together and down now. I don't think the shop will replace it - they claim they didn't have to do anything with the sensor when replacing the hub assembly, but is that false? I just know it was working when I brought it in (physically damaged or not, I can't say), and it wasn't when they finished the job. It didn't sound like they were willing to take responsibility for it, and if I can order one for $171 and replace it myself it won't break the bank. I feel I'm on borrowed goodwill already, with this being the second warranty replacement for the hub assembly, and they (at my request) upgraded me to a Toyota OEM part this time.

    The one thing I didn't notice is where the connector is to unplug/replug the sensor. I think and hope it must be on this side of the fender passthrough hole. If so it should be less than an hour for me to do the whole job.

    What'd ya think? Let it go or push for a free part?
     
  10. KhaPhoRa

    KhaPhoRa Member

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    They would have had to take the part out to do the hub replacement. Unless they did it the really really difficult way of disassembling the hub from the steering knuckle while the whole thing dangles from the sensor wire.. which of course makes no sense compared to just removing one 10mm bolt..


    the Seahawks training facility ?
     
  11. Patrick Wong

    Patrick Wong DIY Enthusiast

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    "...they claim they didn't have to do anything with the sensor when replacing the hub assembly, but is that false?"
    Yes, that is false since the entire steering knuckle and hub assembly is removed and replaced with a new part. Clearly the sensor has to be unbolted as part of that process.

    Since you've gone to the trouble of taking photos, I suggest you remove the RF sensor, take a photo of that, and, assuming you can show a big difference between the LF and RF photos, bring the pictures to Firestone.

    Let the service manager know that you are irritated that you had to document the physical damage to the LF sensor and expect them to either replace the sensor at no charge or give you a $ refund so you can buy the sensor and replace it yourself.

    If the sensor was dropped, that would certainly cause physical damage to the tip.
     
  12. dragonrand

    dragonrand Junior Member

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    Swung by the shop this morning to chat with the service manager. (It's not Firestone - that's just who spotted the problem when rotating my tires - it's actually an independent local shop near my work). I asked him if he could quiz the tech who actually did the work to discover if the sensor was dropped, or hit against anything, etc. He said the owner of the shop had wanted to take care of this one, so he actually did my car himself.

    Long story short, he told the service manager "Make him happy." He thinks it's possible the free play/looseness of the bearing could have allowed the sensor to actually come in contact with the exciter ring. I don't understand enough about the design and mechanics of this to know whether that's possible, if that's where the slop from a worn out bearing would actually occur. Doesn't matter, because he's going to take care of it. They use O'Reilly as their parts supplier, and he said given the multiple failed bearings and the owner's theory of the possible cause of damage to the sensor being the worn bearing, they'll work something out with their O'Reilly sales rep to cover it.

    I passed along the link to the $170 oem sensor at AutoNation for them to use as they see fit when working with their normal supplier. Didn't have a conversation with the owner directly, or I might have passed along the suggestion (which he probably doesn't need from me) to inspect the teeth on the exciter ring for damage. I'm guessing the sensor is usually going to give way before the ring in most cases, so if they swap the sensor and the problems resolve, we can surmise the ring is still in decent enough shape.

    Thanks again, and once the swap occurs I'll post back for the benefit of anyone else who's watching, plus future generations.
     
    thesaint and KhaPhoRa like this.
  13. dragonrand

    dragonrand Junior Member

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    I dropped by the shop after lunch on Friday to learn whether the part had come in or when it was expected, since the scheduling was left somewhat vague. As it turned out the sensor was in and they were available that afternoon, so I brought my car back within the hour for the swap.

    In they end, they covered the cost of the sensor (or split it with the parts supplier), and asked if I'd be willing to pay the labor ($68). Had I known that might be the bargain, I'd have been happy to take the part from them and install it myself. However, the work was already done and I was tired of the hassle, so I didn't argue; I paid the $68 and took my car.

    (I may not take it back there, not because of any attitude problems or lack of honesty at the shop. I think they've been generally-fair minded and willing to work with me, and their hearts are in the right place. I'm just a bit unsettled that more often than not, the wrong part arrives when a part is needed - whether an ordering problem or a supplier problem, I don't know - and I have developed the impression that at least some of their people don't pay enough attention to details some of the time. My Dad, for example, has been taking his VW Diesel there for oil changes, and at least once they've actually put the wrong oil in, and didn't discover it until he asked them to check before taking the car.)

    It's nice to have my regenerative braking back! Milage average is climbing back up again. At 245,000 miles, I've still never had a brake job, and when I (inexpertly) looked at my brake pads when I had the wheel off last weekend, I appeared to still have maybe 1.5-2.0 mm of pad left. Gotta love it.

    I've always noticed that when braking, there is a very noticeable, modest decrease in braking force when I reach abt 7 mph, give or take a little. Since the replacement, I now also notice this sometimes at higher speeds, and the decrease in force is a even bit greater than it was before. Is this to be expected when replacing a speed sensor? Could it indicate minor damage to the exciter ring? Might I need the dealer to bleed my brakes if they messed with a braking component a bit too much when replacing the hub assembly? If it's not a sign of a serious problem and it goes with the territory, I'll just ignore it. I understand that combining regenerative and hydraulic braking to provide a seamless, consistent braking experience is a complex undertaking that won't always feel perfect. But if it's indicative of something else I should address, I prefer to know that.

    Thanks again for all the great advice. Hoping my car easily takes me to 300k and beyond.
     
  14. Brnstrmr

    Brnstrmr Junior Member

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    Well Although this is an old thread I thought I should add my 2 cents as I have just encountered a similar issue. If you look closely at the bunged up sensor you will note that part of the tip is missing and the rest is split. That would be due to the misaligned dust shield hole caused as mentioned by the hub replacement. During re-assembly the edge of the hole shaved of the missing edge and the resultant forces also split the remaing tip. I suspect the shop may have re-aligned the hole when repairing the damage if there wasn't a repeat of the problem. Just my 2 thoughts, but something to look for when doing the hub replacement in your Prius, and probably other Toyotas.
     
  15. Mr&mrs.wiggins18

    Mr&mrs.wiggins18 New Member

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    My vehicle is acting up as well it won't go in ready mode at all we had jumps done but the more we jump it and put it on diagnostic machine the battery drains out again...the codes that came up were p0717 and p3913 after putting gas in it the vehicle still won't start we put it back on the machine to see what was happening and the codes didn't come back up... this is so fustrating we know the dealer is going to charge an arm n leg so if any suggestions that would be great.
     
  16. Patrick Wong

    Patrick Wong DIY Enthusiast

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    1. Disconnect the 12V battery, and fully-charge the battery. You need to disconnect the battery to clear the existing logged DTC.
    2. How much fuel is in the fuel tank now?
    3. After the 12V battery is charged, reconnect it and see if the Prius will become READY.
     
  17. Arkay

    Arkay Junior Member

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    Coming to this many years later. 2014 PiP, Hall effect sensor. However, the basic description gave me the directions to get to the speed sensor. Haven’t solved the abs vsc sensor issue. But making progress.