Buzzing noise under hood

[rhodee90]

I encountered a strange noise the other day when I stuck my key into the ignition. I was about to turn the key to start the 4runner and I turned the key to the on or I guess a/c position. I heard a buzzing noise coming from under the hood, like ZZZZZZZZZZZZZZ so I didn't turn the engine over. I turned the key back into the off position and did the same procedure over and got the same ZZZZZZZZZZ sound. Then I went ahead and started the engine but could not hear the sound, not sure if the engine noise blocked the sound or what. I tried to duplicate the problem since then and haven't been able to. I know if I take it to toyota they probably won't do much if it isn't happening at that time. Has anyone had this problem before?!?

 

[01silverSR5]

I encountered a strange noise the other day when I stuck my key into the ignition. I was about to turn the key to start the 4runner and I turned the key to the on or I guess a/c position. I heard a buzzing noise coming from under the hood, like ZZZZZZZZZZZZZZ so I didn't turn the engine over. I turned the key back into the off position and did the same procedure over and got the same ZZZZZZZZZZ sound. Then I went ahead and started the engine but could not hear the sound, not sure if the engine noise blocked the sound or what. I tried to duplicate the problem since then and haven't been able to. I know if I take it to toyota they probably won't do much if it isn't happening at that time. Has anyone had this problem before?!?

Mine does the same thing. It is normal, I believe that it is the fuel pump pumping fuel or something of that nature. I wouldn't worry about it.

 

[Jeff Kleb]

Me thinks it is the electric fuel pump also. At least that is a logical guess.

:awais:

 

[greasefingers]

It could also be the anti-lock brake system doing a dance? It has an electrical motor or two in it.

 

[Mark86]

Mine does that too. I thought it sounded like a pump. It is not good to leave your key in the 'on' position without your engine running.

 

[ToolmanJohn]

ABS system

Mine has done that since new, also while slowly backing down my driveway when first pulling out., but always when first starting. It's a motor in the ABS sysem but I don't know exactly what it does.

No problems so far in almost three years.

 

[toyota03]

Mine does that too. I thought it sounded like a pump. It is not good to leave your key in the 'on' position without your engine running.

What you guys are hearing is the hydralic brake booster charging up for the braking system. It's louder on the 03-04 model for the bootser motor were metal. On the 05-06 the booster motor seems to be alumimun.

 

[olliebear]

Have the same noise too.

Definite zzzzzz/hissssss, that starts and stops a few seconds later. No effect on the car's performance, and I know it is not the a/c compressor.....has a definite start and stop cycling and not a leak...

Seems to be more prominent starting it up in the morning, but it also occurs while driving...can't hear it when driving normally, but can hear it failtly whne I come to a stop or taking a corner slowly.

 

[noserider]

Heard a similar noise the other day while going slowly up my driveway. The VSC light was flashing at the same time. Is this normal?

 

[earthrealm]

8 yrs after!..yep its the abs pump motor, charging up..............if its going bad, the frequency of pumping/zzzzzzzzzzzzzzzzzzzzzzzzzzz increases

 

[thoff25]

Good to know! Mines making a high pitch every most in a while. Def going bad then…

 

[Raindoh]

Brake Booster Replacement

I just replaced my brake booster with a rebuilt unit from Ebay. It seemed to work fine once I bled it, but over time the pump started running constantly and there is a hissing sound coming from the accumulator. It isn't losing any fluid, is there anyway to fix there leak? Video in link.



https://imgur.com/a/Q8u6hRD

 

[SocalSam]

I just replaced my brake booster with a rebuilt unit from Ebay. It seemed to work fine once I bled it, but over time the pump started running constantly and there is a hissing sound coming from the accumulator. It isn't losing any fluid, is there anyway to fix there leak? Video in link.



https://imgur.com/a/Q8u6hRD

That's the motor going bad. Accumulator may not be holding pressure which is causing motor to run. In my 03, I had loud screeching sound. I swapped in a motor/accumulator from a 04 GS300 which solved the problem. The new to me booster pump runs on key on and every once in a while on the road. I will have to listen for hissing sound which I think is the accumulator losing pressure. My braking action is very good. Before the swap, car would pull hard to right on initial brake pedal application. Car stays straight and stable on the brakes now.

 

[04SR54me]

I would tend to agree. It buzzes then stops when pressure it built. I had to replace mine a few years back. Toyota wanted crazy money. There was a guy that rebuilt the part that fails that was very helpful and it worked out.

 

[DesertTortoise]

That's the motor going bad. Accumulator may not be holding pressure which is causing motor to run. In my 03, I had loud screeching sound. I swapped in a motor/accumulator from a 04 GS300 which solved the problem. The new to me booster pump runs on key on and every once in a while on the road. I will have to listen for hissing sound which I think is the accumulator losing pressure. My braking action is very good. Before the swap, car would pull hard to right on initial brake pedal application. Car stays straight and stable on the brakes now.

So you pulled the accumulator and motor from the GS 300 and only swapped those parts? Not the whole assembly?

How close of a fit is it?

If yours worked, looks like it could be from 98-05 GS 300.

 

[SocalSam]

So you pulled the accumulator and motor from the GS 300 and only swapped those parts? Not the whole assembly?

How close of a fit is it?

If yours worked, looks like it could be from 98-05 GS 300.

Fit is exact. Ebay parts has compatibility chart showing models and years. IIRC, Prius are the same as well. Buy the pump motor and accumulator as a set. Test motor with 12V battery at the junkyard. It should sound quiet. I look for clean units which means it is a replacement and not original. I bought a set to keep as a spare which paid off.

 

[SocalSam]

So you pulled the accumulator and motor from the GS 300 and only swapped those parts? Not the whole assembly?

How close of a fit is it?

If yours worked, looks like it could be from 98-05 GS 300.

Second reply because our forum software sucks...

Yes, pump and accumulator swap only.

 

[DesertTortoise]

Fit is exact. Ebay parts has compatibility chart showing models and years. IIRC, Prius are the same as well. Buy the pump motor and accumulator as a set. Test motor with 12V battery at the junkyard. It should sound quiet. I look for clean units which means it is a replacement and not original. I bought a set to keep as a spare which paid off.

Okay, cool. I went the cheap and easy route this time and purchased a Chinese replacement motor. Eager to see how it works out.
The more I learn, the more I think it will only be the motor going bad. When I opened it up it was full of grease and the rubber around the copper coil was disintegrating.
Tested really high ohm. New motor tests good (low resistance).

Now I need to figure out how to get the brake pedal assembly back together that I probably didn't need to take apart in the first place!
Then bleed the brakes - which I have not done before.

Gaining new knowledge here.
Thanks

 

[Cezar]

Okay, cool
Then bleed the brakes - which I have not done before.

Make sure to read up on the special process when bleeding the rears, it's unique to the 4runner specifically.

 

[SocalSam]

Okay, cool. I went the cheap and easy route this time and purchased a Chinese replacement motor. Eager to see how it works out.
The more I learn, the more I think it will only be the motor going bad. When I opened it up it was full of grease and the rubber around the copper coil was disintegrating.
Tested really high ohm. New motor tests good (low resistance).

Now I need to figure out how to get the brake pedal assembly back together that I probably didn't need to take apart in the first place!
Then bleed the brakes - which I have not done before.

Gaining new knowledge here.
Thanks

Brake pedal assembly is attached to hydro-boost assembly with four bolts and a clip. You will need an assortment of elbows and extensions to reach the nuts. Once you have the complete unit out, replacing the motor is straightforward.

Bleeding brake lines is easy. With your assistant or in my case a tool box, press brake pedal and crack the brake lines until fluid seeps out. Once you get pedal pressure and it is safe to drive, find a safe place to trigger ABS and Traction Control events. This will open the valves inside the unit and get any bubbles moving. Repeat brake line cracking as needed.