U0129 ошибка тойота prius 30

Had a long thread looking for possible causes of sudden appearance of multiple warning lights. thanks to all contributors. I have finally devined a fault code and so starting a new thread to research what troubleshooting flow chart to follow for this code.

As a brief reminder I had Brake, Traction, Power Steering, Hybrid System and ABS warning lights all come on at once with no apparent loss of performance. Car starts and runs (and stops) but doesn’t have speedometer or battery and engine power meter. (the battery state of charge meter is fine).

Regular OBD scanner yielded no codes.

I took it to a friend who had a shop style computer scanner who told me there was a brake communication error but he didn’t give me an actual fault code number.

Dr. Prius gave me this which unfortunately is probably correct but wasn’t recognizable as a standard fault code designation when I posted it in previous thread:

HV Battery ECU Error Code: CC129

I, like many others before me, fell in to the trap of thinking that HV stood for high voltage and there was something up with the high voltage battery independent of this brake communication problem when, in fact, I think Dr. Prius did find the relevant code but didn’t report it in a recognizable way. This turns out to be a pretty significant confusion that folks believe the ‘HV ECU’ is high voltage ECU. Now of course it monitors the high voltage batteries and state of charge as well as many other factors because it is actually the mildly redundant «Hybrid Vehicle Control ECU», sometimes shortened to the less redundant «Hybrid Vehicle ECU» or abbreviated as «HV ECU»

So not realizing that Dr. Prius had got the relevant code, I took it to another friend who has the Snap-on Zeus and printed out the result which was:

HV ECU — Current Codes
U0129 Lost Communication With Brake System Control Module

(same is in History Codes)

Zeus could not reset the code or it the cord came back as quickly as it was reset. If that were the case I would have expeted the History Codes to get an added line for the repeat code but I don’t know if that is how it would work so I’m unsure if it failed to reset or simply threw the code again immediately.

There is an excellent diagram of most ECU component locations posted in another multiple warning lights thread (albeit Gen 2, so I don’t know if anyone has this clip from service procedures for the Gen 3). But it does not show the location of the «Brake System Control Module» nor explain why the convention doesn’t refer to this as the «Brake System ECU».

My guess, given that the electric power braking and ABS all seem to handled onboard the master cylinder in threads I see discussing this, perhaps the Brake System Control Module is onboard or immediately adjacent to the master cylinder on the firewall in the engine compartment. But it is very difficult to see because the master cylinder is buried so deeply under the windshield with lots of stuff in front of it. I’m praying I don’t have to get to it, as it looks like it would take just short of pulling the engine; but maybe someone can talk me off the ledge by explaining that it isn’t as impossible to reach as it looks. Does seem like some parts of black plastic cowling around the windshield wipers could be removed for better access although a bit of a jigsaw puzzle.

The HV ECU shows in the Gen 2 diagram to be on the outside wall of the car passengers side adjacent to the glove compartment.

I don’t see any obvious rodent intrusion and I’ve seen a few threads debunking the idea that the low voltage battery going low is going to set these relatively hard codes.

From my searching, this is a fairly general code (and utilitized in many Toyota and other manufacturer models from what I can see). Most of the threads I see where this code shows up in a Prius also return other C, P or U codes but the Zeus did not find any others. I imagine that techstream would be the gold standard to make sure I’m not missing any and i think I’m going to go with the V-Diag version; but , meantime, I’m looking for a U0129 trouble shooting flow chart so I can see if that code alone has any meaning and how to test for proper functioning of the components and harness involved.

thanks,

brian

I got the U0129 code with a ‘lit up’ dash 2 years ago. Nothing happened to set it off, just tooling down the freeway when the power sagged a lot and the dash lit up. It was my first experience with OBDC and ‘codes’ on modern cars.
I did a lot of digging, went through a bunch of apps, and finally finished with a home Techstream test, The previous owner had it available. He had never had any kind of code with the car.

Ultimately the whole problem went away buy itself, and has not returned. I do not know what to make of it.There do not seem to be a lot of people that get that exact code, or at least people reporting the code and the repair.
Sudden loss of hybrid system while driving | PriusChat

Any chance that could have been transcribed wrong, or something? The second position in a DTC can only be a 0, 1, 2, or 3, not a C.

on Dr. Prius it was listed as CC129 but i’m betting that stands for Current Code 129 and is a shortened version of the full code.which is U0129 as read on the Zeus. Don’t know why Dr. Prius doesn’t list full code. And it is confusing because there could be a 5 digit code starting with C but I don’t believe this was a C code. Dr. Prius had it as HV Battery ECU but I’m pretty sure again that was bad transcription on their part and it is the same fault as U0129.

I see a fair number of threads with the lit dash and the U0129 but they have other more specific codes that drive the troubleshooting. I’ve got the U0129 all by itself.

This might have happened once for a little while 20,000 miles ago, we had some lights, can’t remember if it was the same ones, but it went away quickly. This time I’ve had it for a month and a half so it ain’t going away on its own.

I don’t know if the troubleshooting checks come up in the techstream as well or that is a different resource.

By the time I got it to Techstream there were no more codes. The whole business was new to me, as was the car, so I was doing a lot of thrashing around.

Issue has been resolved on both iOS and Android Dr. Prius App, the CC129 should have been a U0129.
thanks again.

I know it’s frowned on to open an older thread, I am wondering what the solution ended up being and what caused the U0129 code? Replaced my brake module and ABS pump and have same HV error. Can not clear it to do air bleed procedure, my scanner and Techstream error out and will not even start the procedure. Yes I will start anew thread but was really wondering about this one.

Like any U code, U0129 is a communication error code: [something in the car] is saying «hey, I can’t communicate with [something else]».

U0129 is «hey, I can’t communicate with the brake/skid control ECU».

With any communication code, you also want to know who the «I» is in that sentence: what device in the car is saying it can’t communicate with (whatever, the brake ECU in this case). So you want a scan tool that doesn’t just say «somebody said U0129», but specifically says «so-and-so said U0129». Techstream will do that, and some other scan tools or apps will do that. Some other tools and apps just lump together all the codes coming from anything in the car and won’t show you who said which code.

The things in a Gen 3 Prius that can say U0129 are the Power Management Control ECU (which is divided into Hybrid Control and Electric Power Control functions, the U0129 can come from either one), the combination meter, the power steering ECU, and the parking assist ECU if you have that feature.

Once you know which thing(s?) can’t communicate with the brake ECU, then you can look at the network diagrams in the repair manual and kind of figure out where the issue probably is. The multiplex communication / CAN communication system section in the repair manual is where most of the troubleshooting info for that kind of issue can be found.

So I’m kind of saying that there are enough possible causes for comm error codes that it’s kind of a long shot to hope it will be the same cause it was for somebody else … especially if you’ve just got the bare comm code and don’t even know which thing in the car said it. Best to just go ahead and troubleshoot to find what the cause is in your car, and that’ll be the thing to fix.