The great speed sensor mystery

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

 

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.

 

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






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?

 

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?

 

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.

 

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.