Cannot complete replacement brake booster air bleed procedure

George Jung · Nov 25, 2025 at 8:14 PM

rjparker said: ↑

George Jung, post 14 above:

Thank you for the help.

1. Yes. Ive been driving it in this state since. July. intermittently, the cruise control will stop working after ive been messing with things, but happens to come back the next time i go under the hood and mess with things. I cant tell you exactly what i did when it stops working, but that has happened 2 or 3 times now. One time I did skid out of control on the freeway when i was changing lanes and then traffic suddenly was coming to a stop.

When it stops working? And comes back? A failed brake booster loses abs, skid control, regen, mpg and has a hard pedal. When it "starts working" do the dash lights clear, power brakes return, etc?

Forgive me, im referring to the cruise control that intermittently has stopped working. The ABS, TCS, and BRAKE light has been on the whole time.

2.+3. I used the part finder thing based on year and model on Toyota.com, then took the part number it told me and bought it from bamauto.com. When i was removing the old one. I noticed it looked newish, then i recalled that i believe the old owner did say he had replaced the master cylinder before. Im not sure if he did the pump also or
just the master cylinder. The part number on the mastery cylinder was the same. last night I put back on the one that was on there before.

Bamauto.com? I don't believe that is a Toyota dealer and seems to be a dead site now. Dealer sites have a format like "autoparts.hoovertoyota.com" where the "hoovertoyota" portion is the name of the dealer. There are a couple of exceptions like "autoparts.toyota.com"

The Toyota part number is different by tire size in the same year and is different between hatchbacks and Prius v's. In addition the number on the housing is not the actual parts number, it's a housing number which is the same across many part numbers. Used sellers often don't know this and advertise it incorrectly.

Do you have the Toyota box with a label the newest brake booster came with? It's the number you want to verify.
Forgive me i was referring to https://www.bamwholesaleparts.com/ They sell new OEM parts. It appears to be sent via "Brunswick Toyota" The box says #47050-47140. That comes up when i search my vin on Genuine Toyota Parts and Accessories: Official Online Store | Autoparts.toyota.com and Genuine OEM Toyota Parts and Accessories Online - Toyota Parts Deal says its a match for my vehicle option ZVW30.

4. No, that was the only one i believe. I dont recall replacing other fuses at the time.

Normally everybody that blows a 125a fuse also blow six or more other fuses. You could still have a blown fuse but they might be smaller regular fuses.
Ive checked all fuses, they're good.

5. Yes i was able to bypass the fuse in the parking garage of the ferry terminal, then drive back 5 hours to vegas at 10pm on sunday night, after spending like 8 hours figuring out what was wrong. i took like 3 uber trips to auto zone while my poor girlfriend waiting in the car. I dont recall any other issues appearing at that time. I have the replacement 125amp link. I do plan on replacing it soon. I was possibly going to do it today but thats probably not going to happen. Im going to have a couple free days later on this week, im going to get that done then figure out these wiring diagrams and get to the bottom of this brake issue.

I feel there's got to be a bad wire or something somewhere. When i replaced the engine i did snag that harness that runs on top of the transmission, next to the radiator hose coming out of the engine block on the right side. I had to repair wires on the mg1 sensor, and right now im tracing down a bad wire for the MAP sensor. IDK if that harness is at all related to the one going to the ECB, it doesn't look like it.

Blown 125a, replaced engine, modified/ repaired wires and now an intermittent brake booster. It does make wiring, grounds or network buss problems more of a possibility.

Im not going to take it to the dealer. Im going to fix this myself even if i have to replace every ECU in this POS.
Click to expand...

I have finally found something useful in the manual... I found the Page "ABS WARNING LIGHT REMAINS ON". It told me to verify voltage on a28-16 of 11-14 volts and less than 1 ohm resistance to ground on connectors a28-23 to 28. Those all checked out.. So im at a dead end again. I'm going to replace the 125amp fuse tonight, and see if that helps any, though i doubt it.

rjparker · Nov 26, 2025 at 12:26 AM

It would be worth clearing codes, running it again and checking codes again with Techstream.

I would not get too carried away trying to replace the 125a fuse yet. It is very difficult to access. It is possible to bypass it on top but with a 125a added. Checking that the other fuses are good is worth the time.

George Jung · Nov 27, 2025 at 12:34 AM

Replaced the 125 amp fuse... I am now nearly 100% certain this issue is not caused by a faulty adapter, as I resubscribed to GTS and i was able to update calibration on ECU.... So im quite sure my adapter should be capable of performing the brake bleed procedure. Im sill trying to find anything in the manual that is useful.

rjparker · Nov 27, 2025 at 1:20 AM

Codes?

Is this problem coming and going?

George Jung · Nov 27, 2025 at 2:40 AM

rjparker said: ↑

Codes?

Is this problem coming and going?
Click to expand...

No. Since replacing the master cylinder I have been unable to initiate the brake bleed procedure, and the same codes remained. They're attached to the first post of this thread, but The accumulator pressure low and reservoir level are only on when the reservoir is disconnected when trying to do the bleed. When I try to initiate the zero point calibration the lights never blink.

George Jung · Nov 27, 2025 at 3:43 AM

This video here is the type of info i'm looking for... I'm definitely checking all this out tomorrow. It's hard to navigate to this info in the manual without knowing what you're looking for. Everything in the manual is just leading leading me on a loop that always ends on "replace master cylinder"

Cannot complete replacement brake booster air bleed procedure

George Jung Junior Member

rjparker Tu Humilde Sirviente

George Jung Junior Member

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George Jung Junior Member

George Jung Junior Member

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Cannot complete replacement brake booster air bleed procedure

George Jung Junior Member

rjparker Tu Humilde Sirviente

George Jung Junior Member

rjparker Tu Humilde Sirviente

George Jung Junior Member

George Jung Junior Member