2010 Prius Rear Speed Sensor Issue

I'm continuing a conversation here that I started in the wrong part of this forum - see here for my original comment (post #25) and the replies: Driving with a failed inverter coolant pump? | Page 2 | PriusChat

First of all, a big thanks to @Raytheeagle for pointing me in the right direction, and @m.wynn for meeting up with me to read the codes off my Prius. The codes he read for me were:

• P1578 - Brake Booster Vacuum Sensor Circuit, Low Vacuum (perhaps this is just consequential and/or related to the main issue?)
• C2121, C2122, C2123, C2124 - TPMS sensor issues for each tire. I don't have sensors in my winter tires, so no surprise there (although I did perform a hack to get that light to stay off, as mentioned in post #54 at Idea to fool the tire pressure sensors | Page 3 | PriusChat - thanks @m.wynn for pointing me there)
• C0215 - Left Rear Wheel Speed Sensor Signal Malfunction
  
• C1239 - Foreign Object Attached On Tip Of Left Rear Sensor
• U0073 - Control Module Communication Bus Off (assuming that's because the OBD scanner was plugged in?)

So, something was definitely up with the rear speed sensor. Over the past 2 weeks, all the warning lights on the dash (stability control, ABS, and e-brake) - and presumably, the error codes I was getting - have gone off and on periodically, until the past few days, when they have stayed off for about 5 days straight now. At one point I did take the tire off and poke my head around in there, but didn't notice anything out of the ordinary - no wires had any damage, everything seemed secure, etc.

My current best guess is, there's rust built up somewhere that's messing with the magnetic speed sensor. It could also be something to do with snow/ice/etc (I'm just outside Toronto). If it's rust, I'd expect the issue to come back eventually. Anyone else have ideas on that?

Also, my understanding is that the sensor mechanism is integrated into the bearing/hub. I've seen a few posts on here about removing it to replace the whole hub, but is it worth considering, or even possible, to disassemble the bearing and clean out any rust or road crap that's gotten built up in there?

For what it's worth, I'm fairly comfortable digging in and taking things apart. I've changed the spark plugs (lots of fun getting to them on the 3rd gens) and plan to clean out the EGR circuit this spring.

Thanks for any help/suggestions...

 

Thanks guys, looks like replacing the bearing is the only way to proceed. I was hoping I could take it apart and fiddle with the insides, but sounds like that's not really a possibility.

Thanks Mike, I've seen that thread before and it doesn't look too bad. I think I'd go for a Timken bearing, don't really want a cheapo option....

Chap, you are correct in assuming I did some quick Googling . That makes a lot more sense now, I thought it a little weird that the Prius would have a vacuum brake booster since the ICE isn't running all the time. Thanks for the explanation of what I'd find in the repair manual, and that makes a lot of sense, as when the issues are present the cruise control is disabled and won't engage.

I'll update this thread once I take more action... but for now, with the dash warning lights staying off and the terribly cold weather, I'm afraid procrastination is going to get the best of me for the time being. As an old professor of mine used to say, "Hard work pays off, but procrastination pays off now."

 

@Mendel Leisk, I didn't specifically check that the plug was solidly connected, but I took a good look/feel around and nothing seemed loose or broken... I'll have to look at it again at some point. The warning lights came back on a couple days ago and have stayed on continuously so far. The next couple weeks are busy with travel for me, so I'm not sure when I'll get to looking at it again.

 

Finally got my replacement hub in yesterday, so today I went out to tackle the job. Funny thing is, the warning lights have been off for a couple days now with the old bearing. I guess it's more of a "slowly going bad" situation than completely broke. Since I did get the new hub in, I figured I'd replace it anyway.

I had zero issues at all getting the old bearing to come off - after removing the 4 bolts I gave it a good tug and it came right off (being careful not to pull on the sensor cable). I was expecting to need to use ChapmanF's threaded rod method or a mallet of some kind, so it was a nice surprise when it came off immediately. To get the sensor plug out, I intentionally broke the locking mechanism Mendel Keisk mentioned with needle-nose pliers.

The hardest part of the whole thing (for me) was loosening the brake caliper bolts and pulling the rotor out of the caliper - even with the battery disconnected, it was pretty well stuck in there.

But, all in all, the whole task was completed without any issues. Figure I saved myself at least a couple hundred bucks over having someone else do it - $170 USD for a Timken bearing shipped, plus an hour and a half of actual work. Not bad.