Brake Gremlin

[werminghausen]

Thanks Auseeker,

Indeed you are right!
I found the buggers (ABS and TRC Relays) here on the electrical diagram,

There is a ABS Motor and a battery of solenoids (That must be located in the block next to the master cylinder where the 5 plugs are attached).
Also I see the Skid Coltrol ECU in this diagram, a computer that controls the ABS VSC TRAC.

Now it dawns on me. That weird sighing noise during the alarm from the side of the VSC block next to the master cylinder is from this ABS/TRC Motor! It must be.

That means this motor is running during the alarm.
What is the ABS motor doing?
Does the system use a lot of braking power in the process?
Martin

 

[AuSeeker]

The motor runs under normal brake functions but also I would think when the ABS is activated, so if the wrong ABS signals are being sent, wouldn't it trigger the motor to come on to supply pressure for the ABS to function?

 

[SocalSam]

I think the booster pump supplies pressure to the ABS/Trac valve block and the solenoids control pressure to individual wheels as needed. If the MTR relay controls the booster motor and we know the booster motor runs, then it must be the other relay that controls the valve solenoids that is causing problems. Contacts inside relays wear out over time from arcing and mechanical wear. 20 plus years is more than enough to do this. Considering the age of the relays, I think it would be a good idea to replace both of them with new or with known good used.

 

[SocalSam]

I think U19 and U20 are the same. Try swapping them to see if U20 is good.

 

[MikeinNH67]

Auseeker, ok but still plugs were touched. Relays, I wonder if those are the same crappy relays that can stick closed on the A/C clutch. That would make for some craziness I would think.

 

[werminghausen]

Is the ABS Motor the same motor that runs the booster?


I pull the two ABS fuses -ABS Motor 40A- and -ABS solenoid 50A-.
In this case the alarm sound goes away but the dash lights stay on. AND there is no booster any more (It tried to drive but no braking power at all- no booster)..... hence the assumption that the ABS motor is the brake booster pump motor.

Then in the next step I put the ABS Motor fuse back: The dash lights are shining bright but the booster motor works again- no alarm sound and no weird sighing noises- [meaning the weird second signing noise might be the ABS solenoid?] .

From these experiments I conclude that the alarm sound is triggered by the ABS solenoid?


Let me know.

Martin

'

 

[werminghausen]

The motor runs under normal brake functions but also I would think when the ABS is activated, so if the wrong ABS signals are being sent, wouldn't it trigger the motor to come on to supply pressure for the ABS to function?

I think you got a point here.
If the ABS relay is stuck and ABS is ON at all times this would have the pump probably run all the times (as long as the ABS is active).

Why does this trigger the alarm sound? Does the ECU detect the fact that something can't be right if the relay is faulty?



Martin

 

[MikeinNH67]

From your diagram it looks like that motor does ABS and booster seeing both relays tie to it. I would guess it works in conjunction with the solenoids. Relays are cheap, it may be worth replacing one or both. Do you have a picture of one? I'm curious if it's the same brand as the other ones that fail.

 

[werminghausen]

I think U19 and U20 are the same. Try swapping them to see if U20 is good.

Hi Sam,

yes you might be right one of these relays might be faulty.

U18 is the ABS solenoid relay and I guess fuse #55 is corresponding with it.
If the alarms sound goes away after removing #55 then the ABS sol relay might be bad.

Should I swap relays 18 and 19? and put fuse 55 back?

(Well the booster motor will run at all times then as the faulty relay might trigger the booster motor to run)

Martin

 

[werminghausen]

Hi Mike,

here is a picture of my relays.
Blue Cube= U20 (ABS Mtr)
Grey Cube = U19 (TRC Mtr)
Green Cube = U18 (ABS Sol) - This one is most possibly bad
I guess these Relays are all the same...don't know why they have different colors.
You also see that I removed fuse #55 (ABS Sol), which mad the alarm sound go away.
I can try and test the relays tomorrow.
If there is continuity between 1 and 2... well then the relay is obviously bad.
Martin

 

[SocalSam]

Looking at the colorful covers, I think relay ratings are going to be different. Swapping may not be possible. There is a way to jumper at the socket but not sure that is a great idea for ABS module. You may be able to hear and feel them click with key on. Not sure if these relays can be opened but there is a way to open them and burnish the contacts. Testing is good idea.

 

[werminghausen]

Hi Sam
I pulled the green -ABS SOL- relay U18
It has 6 pins underneath but only 4 that can be active (4 in the socket of the fuse box)
I pulled the cover and everything underneath looks brand new. Everything works after testing it.... so I don't know what is wrong.

I also checked the voltage in the relay socket (fuse box) and there was no voltage at then control socket (for smaller control pins #3 and #4 in the diagram). I checked with key in ignition position and with engine running and fuse 55 installed.

So I don't know what triggers the alarm sound when I install this relay back.

Martin

 

[werminghausen]

I am studying the wiring diagram (VSC section page 258 -265). Does anyone know where the basic pressure sensor for the brake booster pump/motor lives that is checking the pressure in the accumulator?
Martin

 

[SocalSam]

Pretty sure pressure sensor is on brake booster / ABS assembly. Look for 89637D-60020.

Oil Pressure Sensor #89637-60020 | Autoparts.toyota.com

I'm starting to think your booster assembly was contaminated with debris when the brake line broke. My brakes pulled to one side before my booster pump failure. When I took my booster / ABS assembly out, brake fluid drained out which likely cleared debris and cured side to side pressure imbalance. (This was an unintended fix but I will take it, lol.) IIRC, I posted a video of an assembly being taken apart and cleaned. Perhaps your pressure sensor is clogged. Suggest remove and flush.

 

[SocalSam]

We are going in a lot of directions. Anything to save $1.4k, right?

 

[werminghausen]

Pretty sure pressure sensor is on brake booster / ABS assembly. Look for 89637D-60020.

Thanks Sam,
I was assuming that the top plug was the pressure sensor, I think your diagram is confirming this, has a triangular shaped plug with rounded edges.

But I cannot figure out/identify where this sensor is located in the electrical VSC diagrams.

Clogging of the ABS/TRC/VSC hardware/ filters and solenoids could be a possibility...and it would make sense.

Saving the 1.4K... yes, but not at any cost ! I want to understand that brake system. But a lot is hidden in the complex electronics and hardware with no good documentation from Toyota obviously.
Do you want me to pull the hydro booster and take it apart for cleaning?
I am ready to do anything it takes...(until I order the new booster).

I have the feeling that things have become worse since I installed the new accumulator... maybe with every additional disturbance more debris has been moving around inside that booster clogging things even more?

Where can I find your video cleaning the interiors?

Martin

 

[SocalSam]

If this guy can fix, you can.

https://www.youtube.com/watch?v=6A8pfxl88PE&t=712s

 

[werminghausen]

If this guy can fix, you can.

Thanks, this video is funny, it reminds me to the time when I lived in the Middle East..people there perform the very same stunts.
I had a T4R in Oman (3rd Gen) and this was convenient because everybody knew how to fix them in the desert.

However... not sure how you can get the dirt out of the passages in the ABS/VSC/TRC block without moving the many solenoids... that would not work properly.
All the rubbber should be replaced once I am there.... hmm.
Including the master cylinder piston ring.

 

[AuSeeker]

If this guy can fix, you can.

Thanks, this video is funny, it reminds me to the time when I lived in the Middle East..people there perform the very same stunts.
I had a T4R in Oman (3rd Gen) and this was convenient because everybody knew how to fix them in the desert.

However... not sure how you can get the dirt out of the passages in the ABS/VSC/TRC block without moving the many solenoids... that would not work properly.
All the rubbber should be replaced once I am there.... hmm.
Including the master cylinder piston ring.

A little expensive for what it is especially if you have to replace the entire assembly later on, but there seems to be aftermarket kits out there as well but they aren't much cheaper.

04493-60350 Genuine Toyota Brake Master Cylinder Repair Kit)

 

[rdruss]

If this guy can fix, you can.

https://www.youtube.com/watch?v=6A8pfxl88PE&t=712s

It is very impressive how people in remote places make these repairs on complex assemblies like this. I guess if you have no other option you "get 'er done"!