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Discussion Starter · #1 ·
Brake Assist & ABS

Is there a way to disable the brake assist feature, but not the ABS? Or...are they one in the same?
 

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they arent one in the same... however, the fuse that controls brake assist also controls other important functions, so there is no easy way to disable brake assist for the track... just an annoyance that takes a long time to get used too...
 

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Discussion Starter · #3 ·
Thanks.

Do you know if they are controlled by 2 diferent computers? Cauz I would have no prob snipping some wires to kill it...before it kills me 8)
 

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redline814 said:
Thanks.

Do you know if they are controlled by 2 diferent computers? Cauz I would have no prob snipping some wires to kill it...before it kills me 8)
not sure if there are any wires to cut per se..... I dont know exactely how it works, but the ECU attempts to recognize a panic stop. Besides brake line pressure, I dont know what other variables the system uses... possibly looks at the speed the car is traveling as well... but this would all be part of the ECU, so no wires really could be cut. maybe a piggyback ECU could be made to override some of the sensors...
 

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Discussion Starter · #5 ·
If I knew how to untangle a wiring diagram of our car....I just might be able to pull this off. Oh well...it was just a thought.
 

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I believe Brake Assist senses rate of pressure increase on the brake lines around the master cylinder area. Look for a connector around the master cylinder and disconnect it. This may disable the input for the Brake Assist computer. I wonder if the brake light will come on. There might be another connector by the master cylinder, this one is for low brake fluid. Check it out and let us know.
 

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Discussion Starter · #7 ·
SilverF16 said:
I believe Brake Assist senses rate of pressure increase on the brake lines around the master cylinder area. Look for a connector around the master cylinder and disconnect it. This may disable the input for the Brake Assist computer. I wonder if the brake light will come on. There might be another connector by the master cylinder, this one is for low brake fluid. Check it out and let us know.
I'll be sure to fish about that area pulling apart connectors and let you know if the car still opperates safely...
 

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I remember reading a while back on this site that... if you remove fuse44 it would disable track, EBD, ABS, and VSC... but brakes will still work
 

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redline814 said:
SilverF16 said:
I believe Brake Assist senses rate of pressure increase on the brake lines around the master cylinder area. Look for a connector around the master cylinder and disconnect it. This may disable the input for the Brake Assist computer. I wonder if the brake light will come on. There might be another connector by the master cylinder, this one is for low brake fluid. Check it out and let us know.
I'll be sure to fish about that area pulling apart connectors and let you know if the car still opperates safely...
:lol: :lol: :lol:
 

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If brake assist and ABS could be disabled seperately Lexus would be facing a big lawsuit, I suspect.

If you could get rid of brake assist and keep ABS, great, but imagine the idiot who screws up and gets rid of ABS and keeps brake assist. He steps on the brakes and "assist" locks up the brakes and he sues Toyota/Lexus and, more than likely, takes a home Lotto-type settlement. Our system awards idiots all the time.
 

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Discussion Starter · #11 ·
I'm willing to play an "idiot" if there is a chance I could be awarded a million dollars :lol:
 

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Defeating the Brake Assist without defeating ABS should be do able. If someone can scan the Service manual section on Brake assist, I can probably figure out how to defeat it. Either by disconnecting the sensor connector or by putting a resistor in line to the sensor to make the computer think that no quick stab of the brake pedal is occurring.

If someone has the service manual, scan in the Brake Assist troubleshooting section and I'll be glad to investigate.
 

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Discussion Starter · #13 ·
So...

I spent a few minutes this weekend removing stuff to see what the effect would be on ABS/Brake Assist. I went to the fuse box under the hood (by the battery). I went for the only fuse 1st. Then, I removed each of the 2 relays. Last, I tried to pull out the funny loooking fuse (yellow bottom w/clear removable top). All each one did was kill the system 100%. That rules out an easy fix.

When I get a chance, I will move my search to the ABS block and the zillion wires that go into it. I'll let you know...
 

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Discussion Starter · #14 ·
Here are the fuses/relays I was playing with...


 

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Got it, Give me some time to review this.
 

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There is a switch called the "Brake pedal load sensing switch". Try disconnecting this switch connector. It is normally open, so by disconnecting it, the computer thinks the operator is never hard enough on the brakes to energize Brake Assist, and this is a separte circuit from ABS. So it should not affect ABS. The wiring schematic does not say where this switch is other than it is component B10, and the location is shown on page 34 (Of the service manual?).

Instead of the looking around the Master Cylinder, I would look around the brake pedal, under or behind it. Don't confuse it with another switch there and that is for the brake light switch. Experiment and see and keep us posted. If you get a "Check Brake" light due to disconnecting the load sensing switch, let me know, I got an idea how to defeat this. But let's first located the right switch/sensor which affects this circuit.

While the wiring schematic does help. It would be more benefical to have the troubleshooting section flow diagram for the Brake Assist and ABS systems. This should be in the manual as well.

First, see if you can hunt down this switch, and disconnect it.
 
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For the "brake pedal load sensing switch", there are 2 wires (Green-white) going into the connector, and 2 wires coming out of the connector (Red-Black).

This is a little different than the stop light switch, which are (Green-white) and (Green-Red). This will help you discern which connector to remove.
 

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Discussion Starter · #19 ·
I will get on it and let you know the cause and effects...

Thanks SilverF16!
 

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Any luck locating the sensor? If not, just ask your LExus Service dept.
 
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