help, code U0129, check hybrid system, costs of repairs

On first glance without studying, just one broken or frayed wire is a jackpot to criminals who run billing at a Toyota stealership. An honest mechanic with actual moral integrity will spend less than 5 minutes to cut the wire, strip the insulation off the ends and repair it by crimping on a butt connector.

Of course if you work for the biggest losers in the future of the auto industry you don't care at all about decency and honesty in car repair, let alone the shift to EVs, so you tell the customer that the entire wiring harness in the car needs to be replaced because that 5 minute repair job of a wire is not as "reliable" as their need to pay for their upside down lifestyle of having more money to pay back in what you borrowed than you're able to make.

 

Did the dealer give you the actual trouble codes they captured from the car? Hopefully that's printed on the diagnostic sheet.

It helps to know what the car's own onboard diagnostics say directly.

A Toyota dealer will be the most expensive place to have this car repaired. Find a local neighborhood mechanic if at all possible. Granted, not all want to deal with hybrids but it is worth the effort.

There is a big expensive wiring harness under the car, it is how the battery connects to the transmission. Not clear to me how this is related to the brake system though.

 

What happened since you posted this in Feb? I have had almost the same problem since Mar 2022 and STILL haven't fixed it! Still driving around. BUT, I need a safety for the lease end buyout and now I actually need to fix this problem!

I did a LOT of research on this since a dealership in another part of Ontario quoted me over $6000 to replace the BBAMC. They didn't add on "Damaged Wires" or "Main Harness". Also the "Brake Booster with Master Cylinder Assembly" part they quoted me was over $2500 a year ago and somehow is now over $4500 for the part!! That whole assembly and the labour is supposed to be under $2000 total and is less than 3 hours labour on the TSB for some years of Prius C.

There is a "Customer Support Program" to replace 2012 Prius C "R & R Brake Booster Assembly With Master Cylinder and Brake Booster Pump Assembly" and that shows 2.3 hours of labour (see below).

Have you called Transport Canada to report this defective part? You should and mention the "Customer Support Program 21TE01" in the USA

Transport Canada told me that it would only become a recall if more people report this (Prius C owners).

You should also call Toyota Canada and complain and show the above Customer Support Program for the USA. I was told that my 2016 Prius C BBAMC was "defective", but I have to pay the $$$$$ to replace it, though Toyota Canada did offer me a (fake) discount of about $1000. Great, $1000 off a $6000 repair that is supposed to be under $2000! I save -$3000. I am very unhappy with Toyota sending out faulty Brake Boosters and making us pay for that! They told me that if my Prius C was in that 2012-2015 range they would "do more". I might have even seen a recent "Customer Support Program" for your year that applied to Canada!

ALSO, look for the petition for a Defect Investigation from a Toyota Dealership President named Roger Hogan to the US Department of Transportation from September 2019 INBC-DP19004-77358 . Which I found was denied after the petitioner mysteriously withdrew the petition (see the federal register website).

I got the Service Manual for my 2016 Prius C and it says when you have the U0129 DTC to first check the CAN BUS resistance in the connector from the BBAMC before replacing the BBAMC, which the dealership %100 did NOT do, because it involves taking apart a bunch of things to reach the BBAMC connector to the CAN BUS. I did that.

Other information I found says that a ground fault to the BBAMC is the MOST common reason for the DTC U0129 "lost communication" to the BBAMC/Skid Control. I am working on that now, since of the 6+ grounds to the "Skid Control Unit", some are hard to get to. I really hope I find a bad ground and that fixes everything.

I also came across the possibility that a speed sensor in one (or more?) of the wheels could be damaged or something. I might try looking at those speed sensors before moving to the last resort of replacing the BBAMC, which I will NOT be doing at the dealership!

It would be cheaper to buy a Techstream Lite and a used or even new part myself and do it myself. Will save $4000+ and own a Techstream (well some sort of J2534 interface and maybe have a subscription to the Techstream software for some amount of time. The year of software for over $500 is a bit much. Still, cheaper than the dealership. I am still making sure I will be able to do the whole process myself, since Toyota seems to have made it very difficult to get anyone but "authorized Toyota hybrid technicians" to do so many things on our cars. I keep looking for DIYers replacing this BBAMC on a Prius C! Haven't found one yet who said "yes, you can do this at home with xx equipment and interface".

ANY more info about this would be appreciated by ME and I am sure OP!

Please report Brake Booster Assembly with Master Cylinder defects and DTC U0129 so we can get a recall and not just a selective "Customer Support Program"! It looks like so many Toyota Prius C and similar models in North America have defective Brake Booster Assembly with Master Cylinder problems.