brake actuator resistor

The brake actuator on our 2006 Prius (95K miles) was activating (pump turned on) every 20 seconds or so. I used AutoEnginuity (AE) software to monitor the pressure of PACC (accumulator pressure sensor) and the pressure dropped rapidly once the sensor voltage got up to around 3.1 volts; therefore, the pump would activate again and this cycle would keep repeating as long as the Prius was turned on. Therefore I decided to replace the brake accumulator and its associated resistor. I purchased a new brake actuator and its associated resistor from Toyota. The brake accumulator replacement went well but when I tried to locate the resistor to replace it, I was dismayed to see that the old resistor is very hard to access (even though I took most of the dash apart to find it). In my 2006 Prius, the resistor is on the driver's side near the body and high up under the dash. I think I understand the reason for matching the resistor value with the resistance of the pump windings but I am going to use the old resistor and see how noisy the pump is. BTW I referenced Toyota website (TIS) for how to do the replacement procedure and now I am going to see how good AE software (latest version) is at bleeding the various components. This is FYI for anyone replacing the brake actuator and wanting to know where this resistor is located and how difficult it is to access. If anyone knows a fairly simple way to access this resistor, I would be interested. Thank you.

 

Pictures attached.

 

I can't get a picture of the resistor that would show it or provide a meaningful representation of where it is without taking off the "top" section of the dash and if I do that I might as well replace the resistor.
FYI: The resistor that came with the actuator is 193.6m ohms which I believe is .1936 ohms. My understanding is that this resistor is in series with the pump motor and is probably "tuned" to this pump motor. This resistor will change the voltage drop across the pump motor, the rpm of the pump motor, the total current flow and; therefore, probably optimize the rpm/noise from the motor. This is a low resistance circuit and will pass significant current so this resistor has a heat sink (the current to the motor is the same as the current to the resistor). BTW the picture of the brake actuator is of the old one. Thank you. (I had the resistor value wrong so I updated this post).

 

It isn't feasible to mount the resistor elsewhere and I can't get to the existing resistor (won't pull the top dash...yet) so reading the resistance value on the resistor can't be done.
Both the old and new actuator and resistor are Denso.

 

I started the process for bleeding the actuator, wheels, etc. and the pump motor doesn't sound noisy; it isn't as quiet as the old one but it sure works better. The output of the PACC sensor (accumulator pressure sensor) is 3.61 volts and more importantly it holds steady until the brakes are applied. When I get more ambitious I will replace the resistor, compare values and report on noise levels.

 

Yes. I plan to do every step specified in the Toyota procedure for replacing the brake actuator. I am using Autoenginuity (AE) so this should be interesting. So far the procedures in AE don't accurately line up with the steps in the Toyota procedure so I must understand what each step does and how I know it is done properly.

 

Did the brake bleeding and discovered some of the AE instructions were wrong (you can't have the pump relays (#1 and #2 installed when bleeding the back brakes). The real problem has surfaced when I tried the initialization of the linear solenoid valve and the calibration. The reset went okay but the signal check failed with DTC 1203 and 1345. The 1345 (solenoid valve was reset) makes sense but ;the 1203 indicates a mismatch or communications failure. Will investigate what is going on and why DTC 1203.

 

Ops, my bad. AE works fine; the initialization of the linear solenoid valves worked fine once I understood which option to select within AE. Prius is braking fine and actuator is working fine. I bleed the wheels many times to try to ensure no air was in the line(s).

 

The motor in the brake actuator is "turning" on to bring the braking pressure up to provide adequate braking. If the motor is turning on frequently, then the actuator has a leak or brake fluid is leaking somewhere in the braking system. In my case there weren't any external leaks; the leak was internal to the brake actuator. This is an unacceptable safety issue for me. The actuator leak will not get better; the worst case scenario is bleak and I always want my brakes in very good working condition. Good luck.