Help needed: interior “horn-like, loud buzzer” sound

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Hi all,

My parents’ ‘06 with close to. 180k on it experienced a very loud “horn like” sound while using cruise control the other day. It was a steady sound, and only lasted about 5 seconds but it was loud enough that they pulled over immediately to check things. They believe it was coming from the dash area. It’s possible it stopped on its own but also possible that my Dad stopped it while he was pushing cruise control buttons while pulling over.

The sound is gone now and everything seems to function normally.

Any ideas? Search didn’t really turn up much of anything other than a possible imminent ABS failure but there was no light and ABS still seems functional.

Help is very much appreciated!
 

JunkCrzr89

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It’s a warning that either the brake fluid is low or the brake booster is failing.
 

JunkCrzr89

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@Mike NXP and @JunkCrzr89 : that was my first thought, but wouldn't any brake issues have triggered an ABS light? I'll have them check the fluid level (or have someone do it, they're almost 80!).
Low fluid would trigger the parking brake light, but the ABS light is not always triggered when the booster assembly fails.
 
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Bulbs do burn out too.

If you or your parents are driving this before you figure out the issue, make sure to do the same thing as before, pull over immediately.
 
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An easy way to test this is to have the engine running, transmission in Park, and pump the brakes 15-20 times until you hear an audible alarm. If this is the same alarm that they heard before, the brake booster needs attention ASAP. If this is not the sound they heard before, I am not aware of what else has an alarm in the dash....
 
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@KliersLC : thanks for that simple check, just had my Mom do it and the sound was quite different (loud horn type they experienced vs beeping with ABS light from just now). They are now reconsidering whether they were simply hearing a loud truck horn (I mean, they're closing in on 80, hearing isn't great these days!).
 

JunkCrzr89

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Horn sound from brake booster means internal seal in master cylinder is bad, and cannot hold high pressure fluid from accumulator. Non replaceable part, you need a new master cylinder assembly sadly.
Master cylinder rebuild kit is available from Toyota for like $50. The MC is typically not the culprit when that alarm sounds…
 

ramangain

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Master cylinder rebuild kit is available from Toyota for like $50. The MC is typically not the culprit when that alarm sounds…
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There are two distinct brake booster related sounds that mean completely different things.

1. You get an ABS light on the dash followed by an alarm, 99% this means your booster pump motor failed

2. You hear a loud horn like sound coming from the brake booster itself, when under pressure, usually followed by bubbles in res. This mean the internal seal is no longer sealing, not the master cylinder piston! You cannot fix this with a rebuild kit, you have to buy new MC. See pics below.

Internal non replaceable seal in yellow
brake-master-inner-seal-pluger-jpeg.2385173


Diagram showing internal seal

brake-system-c-jpg.2385181


Only thing a MC rebuild will help is with pedal feel, or sticky brake pedal.
 

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