[Erik Steinbring]

I have come to the conclusion after hours of internet research and multiple testing sessions that the accumulator is on its way out on my 04 SR5.

The booster pump is working and all the dash lights go out as soon as the accumulator hits pressure. However, after an hour the codes are back reading low pressure. When I pump the pedal around 10 times the lights also come on. Once the pump catches up the lights go out.

I can purchase the Accumulator for $256 plus shipping online. It is a special order item which will take a few days to arrive. Upon my research I noticed that a lot of auto manufacturers make changing the Accumulator a painless process. Basically depressurize, unscrew the old/bad accumulator and screw on the new one. Since the system is closed usually no bleeding is required which I found odd. I was wondering if it was the same for the 4Runner or could be done in the same manner without having to disassemble the whole system from the firewall.

Does anyone know where I can find the procedure to just swap out the Accumulator? Has anyone just replaced the accumulator?

[Erik Steinbring]

Bump

[Kmvreter]

Most here have gone with the full master cylinder & accumulator & pump change as an entire unit. Not sure anyone has done just the accumulator. Check the FSM pages I attached here: Possible ABS sound. I think the overhaul pages are too big to attach here.

@BlackWorksInc has experience with this.

[Kmvreter]

Here are the pages:

[Erik Steinbring]

KM,

Thanks for the pages. They show the whole system off of the firewall. It just seems like a lot of work to replace a part that screws in and out on the topside.

I would consider replacing the whole unit but the motor is pressurizing the system fine, all lights bells and whistle go out while in park and remain so driving short distances. The lights pop on after a few pedal pumps which leads me to a weak accumulator. Every time I shut the vehicle down within a hour the Accumulator low pressure code pops up upon restart. Also with the engine off within 10 or less pumps the system is completely depressurized. From what I have read if the accumulator problem is not repaired the booster pump will be the next to go due to more than normal cycling.

I am just a shade tree mechanic, is there something else I should be looking or testing for?

[BlackWorksInc]

Huh... I could have sworn I put a .pdf link in the thread? I guess I didn't...

Anyways, here's some pictures of a tear down I did on my old unit:

HydraBoost Brake Assembly

Sorry I didn't get around to your thread much this week, I have been busy at work and afterwards all week.

Originally Posted by Erik Steinbring

KM,

Thanks for the pages. They show the whole system off of the firewall. It just seems like a lot of work to replace a part that screws in and out on the topside.

I would consider replacing the whole unit but the motor is pressurizing the system fine, all lights bells and whistle go out while in park and remain so driving short distances. The lights pop on after a few pedal pumps which leads me to a weak accumulator. Every time I shut the vehicle down within a hour the Accumulator low pressure code pops up upon restart. Also with the engine off within 10 or less pumps the system is completely depressurized. From what I have read if the accumulator problem is not repaired the booster pump will be the next to go due to more than normal cycling.

I am just a shade tree mechanic, is there something else I should be looking or testing for?

Did I ever get you information regarding how the pressure sensor works? Or did you ever get the chance to test the sensor and verify it is working correctly?

[Erik Steinbring]

@BlackWorksInc

Thanks for your reply. You didn't give any info regarding the sensor operation. I am not certain as it is VERY vague as to whether the "Pressure Switch" is the same as the "Pressure Sensor". Any info would be greatly appreciated as I have not ordered any parts yet.

I did perform the shade tree test and disconnected the connection to the pressure sensor to see if a new code would be thrown and one was. Once I reconnected the pressure sensor the code (code 46 do not have my notes in front of me) went away.

Currently the accumulator needs a kick start to fire up the pump with light tap with any hard object, currently a small river rock is working well.......one or two light taps on the top and the pump fires up, pressure is obtained, all the dash drama goes away and all is good.................however retention of pressure is short lived.

"The Bomb" I think is the culprit of the issues as everything I have read and see seem to point to a failing accumulator. Please let me know your thoughts are.

[Erik Steinbring]

Bump

[Erik Steinbring]

I was able to pick up the booster pump assembly with a accumulator. Since it is independent of the master cylinder and ABS module, is it possible to replace these components without having to disconnect and remove the master cylinder off the firewall? I have looked at the pictures and while separate it appears Toyota did not leave much room to work.

[BlackWorksInc]

Originally Posted by Erik Steinbring

I was able to pick up the booster pump assembly with a accumulator. Since it is independent of the master cylinder and ABS module, is it possible to replace these components without having to disconnect and remove the master cylinder off the firewall? I have looked at the pictures and while separate it appears Toyota did not leave much room to work.

I disassembled my old one on the bench, I'm not sure you can do it on the vehicle very easily.

[TurboProp56]

Originally Posted by Erik Steinbring

I was able to pick up the booster pump assembly with a accumulator. Since it is independent of the master cylinder and ABS module, is it possible to replace these components without having to disconnect and remove the master cylinder off the firewall? I have looked at the pictures and while separate it appears Toyota did not leave much room to work.

@Erik Steinbring Did you ever make this repair? I want to know if I can just swap out the accumulator.

[BlackWorksInc]

Originally Posted by TurboProp56

@Erik Steinbring Did you ever make this repair? I want to know if I can just swap out the accumulator.

You can do it, but I don't think it's possible with the unit mounted on the firewall.

[TurboProp56]

Originally Posted by BlackWorksInc

You can do it, but I don't think it's possible with the unit mounted on the firewall.

roger that. mine is vibrating constantly and has now started to screech, like a long turkey call. i hope its just the accumulator ($300) and not the pump assy ($1000+) no warning lights or loss of brake pressure though.

thanks

[Erik Steinbring]

I changed out the booster pump and accumulator assembly, bought it from a used parts house on E-bay. They gave a 3 month warranty on the part, been two years and still working great. It took me about 3 hours from start to finish to perform the swap out. The hardest part was putting a small cotter pin back in place upon reassembly due to tight quarters under the dash.

I later tried to remove the accumulator off the old assembly, just for fun without much luck. I appears there is a special wrench that is required to make the process easier. As Blackworks said it is possible.

[Erik Steinbring]

This was the E bay seller: ABS Brake Pump Master Cylinder Booster Assembly 05 09 Toyota 4Runner STK A48515 | eBay

At the time back in 2014 he was selling the booster assembly (pump and accumulator) for $275 shipped.

Not sure if he still offers just the assembly anymore or if you have to buy the whole thing, master cylinder and all, might be worth asking.