Brake System Issues (ABS, BRAKE, VSC)

To start: recently my Gen 2 prius has had some reduced pressure when initially starting the car and shifting into reverse. Almost as if the accumulator pump was not running as it should on door open.

Then a week or two later, I would notice the BRAKE, ((!)), ABS, VSC lights would not turn off until the pedal was released during start up. So the vehicle would be powered to ready, lights stay illuminated until I released my foot and then they turned off.

Now a week later, my BRAKE, ((!)), ABS, VSC stay on, with reduced braking force. I have attempted the OBD II 4 / 13 pin reset and blink out and found codes:

Spoiler: Blink Out Codes

BRAKE 36 57 66
ABS 42 95
VSC 43 45 62 63

BRAKE 36 - Foreign Object is Attached on Tip of Front Speed Sensor LH
- Left front speed sensor
- Speed sensor circuit
- Sensor installation

BRAKE 57 - Accumulator Low Pressure
- Brake actuator assembly (accumulator pressure, accumulator pressure sensor, pump motor)

BRAKE 66 - Linear Solenoid Valve Offset Learning Undone
- Initialization of linear solenoid valve and calibration undone

ABS 42 - Open in IG1 / IG2 Power Source Circuit
- ABS NO. 1 relay
- ABS NO. 2 relay
- Harness and connector
- Skid control power supply circuit
- Brake control power supply assembly
- Hybrid control system

ABS 95 - ECM Communication Circuit Malfunction
- Skid control ECU

VSC 43 - Acceleration Sensor Stuck Malfunction
- Yaw rate (deceleration) sensor
- Skid control ECU

VSC 45 - Acceleration Sensor Output Malfunction
- Yaw rate (deceleration) sensor
- Zero point calibration not done
- Skid control ECU

VSC 62 - Front Hydraulic System RH Malfunction
- Fluid leakage
- Brake actuator assembly
- Disc rotor

VSC 63 - Front Hydraulic System LH Malfunction
- Fluid leakage
- Brake actuator assembly
- Disc rotor

I checked brake fluid level all is normal, battery is new (replaced in last 12 months) no sign of parasitic drain. The accumulator pump can still be heard, albeit not as often.

These codes make me want to assume my Skid Control ECU has died, thoughts? Thanks for any help!

 

I've tried my android OBDII cheap-o reader and Autozones reader with no codes. (why I translated the blink codes).

I'm pretty DIY, I do all the work for family's vehicles, but the prius braking system is a bit complex and I am hesitant to drop cash on a Techsteam. I did read there might be some electronic configuration regarding replacing ECU, accumulator, or other sensors.

and I am located in the DFW metroplex. Some other information: 2004 Prius with 181k miles, original brakes.

 

All the codes prefixed by BRAKE are the ((!)) blink out. Thanks for the information about ABS vs ECB. I can upload a video of my codes if someone would like to crosscheck them.

 

Yeah I can try a few more chains. I use Torque, I have not tried Dr. Prius app yet.

In regards to the mini-vci, I did not realize the software / connector combo was so cheap. I've read that v8-10 is best for this generation and that it might have to run on Win7.

In the meantime I've ordered a used Skid Controller ECU.

 

Techstream arrived:

Code:

C1256 - Accumulator Low Pressure
C1300 - ABS ECU Malfunction
C1344 - Hydraulic System (RL)
U0123 - Lost Communication with Yaw Rate Sensor Module
U0124 - Lost Communication with Lateral Acceleration Sensor Module
U0126 - Lost Communication with Steering Angle Sensor Module

Obviously C1256 is the biggy. After looking at the trigger conditions it aligns with my previous experience. Low pressure at start up, while I rapidly shift into reverse and provide speed input. I got in, in a hurry, started to ready and shifted to reverse felt lack of pressure and triggered code.

Why was there low pressure? Not sure, it's my understanding the accumulator builds pressure on door open, maybe I didn't provide it enough time or it's on the way out.

I cleared the codes and drove it around the neighborhood, and for good measure calibrated the sensors on level ground in accordance with repair manual. We'll see if it returns. I would like a second trigger before replacing the pump to reduce the odds of it being a fluke event.

 

Well the codes came back and there is an audible difference in accumulator sound. It sounds weaker now so definitely a failing accumulator, just ordered a refurbished one.

 

I bought a $100 VXDIAG software came provided.

Turns out it wasn't refurbished just pulled from a yard. Was caked in crud. Installed it the other day but am having some unusual behavior. I bled the system multiple times and it seems like there's an unlimited supply of air. (possibly a leak or loose connection)

The brakes seem to apply unevenly (similar feel to a warped rotor rapid on/off), pump makes unusual sounds. Still investigating what I did wrong.

 

So replaced actuator pump.. Bled that night and for good measure as I wanted to be sure all the air was out of the system bled again in the morning.

Now sometimes the pump is audibly louder than other times. It runs almost non-stop and got some new codes:

Code:

C1253-136 - Hydro Booster Pump Relay
C1256-143 - Accumulator Low Pressure
C1391 - Abnormal Leak of Accumulator pressure

I can't see any leaks.. But that's my first inclination was there's a leak and air is entering the system somewhere. After driving it 80 miles or so the brakes have not faded, I feel like if there was a leak we would have lost all pressure by now..

The brake application does feel different, pedal feels different at times and at low speeds the application doesn't feel all that smooth. On the first day it felt almost like warped rotors however that feeling isn't as present anymore.

What should I do? Another bleed? Relay test? How much fluid does it normally take to completely remove all air from the system after accumulator replacement?

 

So if it's an internal leak then the used accumulator I got is bad. What if I moved the motor from my used one to my old one that died?

In addition my prius makes loud buzzing when stopped if this is any indication of anything. Here's a video:

 

My bad mixing up words.. Yes, Ive replaced the actuator pump with a used pump online. Now I'm trying to debug either a faulty replacement pump or an installation issue.