Have an '03 4runner that has the persistent buzz or squeal coming from the area of the ABS booster pump system when brakes applied. It is not the standard hum of the system while pressurizing. Have replaced the ABS motor, o-ring on accumulator, & piston on MC. Brakes function, but maybe a little soft & no alarms.

What are the signs that the accumulator is bad or failing? Can the dealer or qualified mechanic test the system to diagnose the issue? Was looking to take truck to dealer & have them run diagnostics on the truck, but not much confidence in them working on a 19 yr old truck. So cking with this group first before adding more costs to this dilemma. Have seen other posts mention using Techstream for analysis of system, but when asked the dealer about that, the rep said they did not know what Techstream was & they could go through normal route to ck for codes.

Was also looking at replacing the pump. Same question, is there a way to tell if pump is failing? If can find pump only, could replace the accumulator & pump, but maybe there is another issue going on. Was also thinking that maybe this is a fluid issue within the system & I have not removed all the air.
Tks

sounds like a failing brake booster. happened to me. i bought a used replacement for about $500 and had a shop install. about 100k miles ago. now the abs sensor is going bad, so will be doing it again.

You can't just buy the new pump itself but you can buy a new OEM pump assembly, which includes the pump, motor, and accumulator for a little over $700, you can sell the used motor you have replaced, it's usually the most common failure and you should be able to find a buyer here on the forums to get some of your money back.

2003-2009 Toyota 4Runner Power Brake Booster 47070-30060 | Toyota Parts

But if the master cylinder part goes bad later you will have to replace it, which costs a little under $1200

2003-2005 Toyota 4Runner Brake Master Cylinder 47025-60081 | Toyota Parts

However if it were me I would replace the entire assembly which you can get for a little over $1300 and never worry about it again, you can also as mentioned go with a used assembly from eBay or a savage yard for much less but you may end up replacing it again down the road.

1998-2003 Toyota Actuator Assembly 47050-60010 | Toyota Parts

AuSeeker, yes, have considered those scenarios, just that pretty deep into this for a vehicle planning on selling &the added costs 1/3-1/2 value of truck. Sometimes can find the motor/pump used or aftermarket units, but do not want to end up in same scenario. So, was looking to try least painful route for where am now if can figure out what/where the sound is being created. That is why asked about if anyone had a tip on or knows what symptoms are when one of these parts are failing. Probably will go with rebuilt or new, if can, entire unit(MC) & move on.
Tks for responding

Spending $10 or so at your local auto part store for a mechanic's stethoscope should help you pinpoint where the sound is coming from.

If you're planning on selling it I would just go with a used assembly from eBay or salvage yard, especially if you can get a 6 month to 1 year warranty on the used assembly.

Yes, tried a stethoscope & do not think the noise is from the motor. Could not get on the pump too well to ck it, so may try again. Can pick up an aftermarket pump & motor which may take care of the pump question or go the entire system route if can find one in decent shape.
Do you know if the system will still need to be checked out by dealer or a Toyota tech to make sure system has been bled correctly? Have read many threads on bleeding w/ & w/o the SST & have bled the MC before also. This was another reason to take to tech to see if there is something that is failing or system is just not purged correctly. Guess will not know until do it. Tks again

Forgot to add sound of noise. Below are 2 vids of the sound
4RNR3 - YouTube
4RNR1 - YouTube

From what I've read from others here when they take their T4R to the dealer for ABS/master cylinder issues, the dealer always says all they can do is replace the entire assembly, they will not just replace individual parts of the system, so I fear you won't get them to tell you which part of the system is bad.

That being said, I don't know what that sound could be, but it's happening too often to be the pump/accumulator unless it's not build up pressure at all, in which case your brakes would not be working very well at all.

As far as you saying the brakes are a little soft and may need bleeding, have you done the "40 pumps" when doing the bleeding?

If not you need to try that, it has solved the soft pedal for most all who have done that procedure while bleeding, just do a search and several topics will come up.

I doubt you need to have a dealer do the bleeding if you haven't drained all the fluid out of the ABS module on the side of the master cylinder.

I think there's a fuel damper in the fuel line in that general area around the valve cover that sometimes makes noise when it's going bad but usually it's a clicking noise, so not sure if that could be the cause of the noise or not, anyway as loud as that noise is I can't imagine not being able to pin point where it's coming from with the stethoscope, it should about blow you ear off once you touch the probe where the noise is coming from!!

having the same issue, did you end up replacing the whole thing or figure out what it was? don't want to spend $700 on new pump/motor/accumulator if it's just one of those things.

That sound is pump failure. Pump can be replaced by itself. When mine went out the first time, I replaced pump and accumulator assembly with a junkyard part for $60. It worked perfectly but lasted only a year. In fact, my new to me pump just locked up a few days ago so I replaced it again with a spare. Bleed without scan tool is easy:

https://www.youtube.com/watch?v=JM5A8PnjS7I

When buying from the self serve JY, test the pump with 12V. It should be relatively quiet and almost like a sewing machine. First time I was in a pinch and took what was available. That pump was louder. When I looked for a spare, I took my time and found a good sounding one. In the car, it sounds like a new motor. This part can be found in other Toyota models. I found mine in a wrecked Lexus GS.