ABS sensor issue - Anyone know this stuff

Is it the ABS sensor or what is the cause that caused ABS light to flash ?

I suspect that: mechanic during the changing the bearing has messed with hydraulics. So, while wheel and brakes were disassembled he opened the door (which activated brakes system, pressurized the system, pumped the fluid ) and the piston shoot through caliper causing air to be introduced to the hydraulics and then they did put all back (without proper procedure to bleed the brakes using scanner tool etc?).
Or- mechanic deliberately opened all hydraulics to remove calipers and to have more free space to work on while changing the bearing (without knowing that brakes/hydraulics on Prius are specific and need specific knowledge/ procedure and sometimes special scanner tool to work on them). I am talking brakes, because all this part is assembled together so you need remove part of accessories to get into other ones while working on them.
Can you asses if there is anything wet around the wheel area. Look for oily spots (jack up the car and remove the wheel first). I mean, can you see if brake fluid leaked anywhere and caused stains on the other brakes elements ? Such as this: http://www.alanauto.com/pics/1800ES_VAR_0511093.jpg (borrowed picture from internet)

Elements should be dry.

I would take extreme caution, do not drive the car with any speed over 20-25mph until brakes are 100% fixed. Use emergency brake if needed (the pedal on the floor - just press it slightly and if it click and lock make sure to don't leave it locked while still driving.

Recently I did some checks on my front wheels, take a look at my post number #28 at this link:

I am not sure if you are talking about rear or front wheel bearings, anyway you can compare your elements to seek wet spots. There shouldn't be any wet spots anyway.

Brake system failure after changing front pads

-don't mind the title, I just used this thread.

you will see pictures (prius is from 2005) and you will know what means dry brakes elements. the area should be dry as on my pictures. If you can notice any changes in color, such as oil was split there you will know that there is air introduced to the system and your brakes will need to be properly bleeded (toyota garage I suppose).

*I would take extreme caution, do not drive the car with any speed over 20-25mph until brakes are 100% fixed. Use emergency brake if needed (the pedal on the floor - just press it slightly and if it click and lock make sure to don't leave it locked while still driving as you will cause damage to rear brakes.)

I think I noticed you are taking about rear wheels. In america your car has drums on rear (mine has calipers and pads). You will have a bit more pain to check rear, and you need extra caution when you lift up the car to assess for wet stains. Ideally I would take it to the nearest shop to lift up the Prius on the car the lift (possibly remove the drum) and ask tech to tell you whether he see any wet spots around the drum where previous tech was working on. I suspect that tech removed rear brake cylinder as a part of procedure to change the bearing. However if not used correct tool to bleed the hydraulics system then this caused the problem and ABS light to flash. It's just my guess.
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So: if you can ask shop to asses for free whether there was a leak then you will still need go to toyota dealership to read the codes and to remove the air from the system.

If you don't know shop that could asses for you for free, bring the car straigh to the dealership to rectify the problem early.
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It is commendable the shop is willing to do this for you. But it does seem like a coincidence, even though problems with wheel speed sensors are common. What is the trouble code?

 

Yes it is extremely helpful. The car is in the special emergency brakes mode therefore apply limited pressure to front brakes. Do not drive this car. Other posters may tell you other opinions. Can you get it towed for free or under insurance straight to the Toyota dealership to read the codes and fix you brakes system?

Where are you based? possibly there is a forum member that could help you or perhaps guide you.
The dealership will charge you over $300 for bleeding the brakes.

Important thing is to connect the scanner and read the codes, as seilerts said, tell us what error code can the Tech read?

 

Thanks for your update.

What does ''removed'' mean?

1) does it mean that were removed and put on the bench while working on the bearings (unscrewed from the hydraulic hoses)

2) does it mean that were removed and while still attached to the hydraulic hoses somehow pushed to give space to work on the bearings

I would like to clarify that part.

Good News that you will get the trouble code let us know.

 

It would be nice to get the code. Some vehicles use a Hall Effect sensor to pickup rotation from the disc. It might be they just forgot to plug the connector back together after taking everything apart. Not sure about late model Toyotas though. Code would help narrow that down.

 

Have they let you drive the car home even when they knew only front brakes are working?

 

Usually the caliper is left hanging off the strut, once removed from the rotor. But this brings up an interesting scenario. The piston tends to creep forward once the pads aren't touching the rotor. It is possible, if not likely, that the piston had to be compressed to get it back on the rotor once the repair was done. But, compressing the piston without disabling ABS will cause a pressure sensor brake DTC. I wonder if that is what is going on here. If so, all that is required is to reset the code.

 

Definitely. This happens all the time.

 

C0200 is the front passenger side wheel speed sensor. Was that the side that they worked on?

 

DTC C0200/31 Right front wheel speed sensor signal malfunction:

Here is paperwork regarding this error:
Google: DTC C0200/31 Right front wheel speed sensor signal malfunction

Inspection procedure:
-Check harness and connectors (mementaty interruption)
-Read value of intelligent Tester II (Front Speed Sensor)
-Inspect Speed Sensor and Sensor Data Serrations
-Inspect Front Speed Sensor (Make sure there is no loosesness at the connector)

It's a nice read.