Subtle brake problem.
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Driver School Candidate
Joined: Nov 2011
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From: Outside US
Subtle brake problem.
I have recently bought a second hand 2008 RX400h. No need to tell the other forum users how splendid the car is,
However a slight problem har surfaced and I wonder if anyone else has experienced the same thing:
When braking gently, after a very short period of retarding the car, the braking effect is markedly reduced in spite of constant pedal-pressure. (More or less like when the ABS engages on very icy surface. Applying more pressure to the pedal increases the braking effect, but particularly when driving on icy conditions this is annoying as you dont know or feel if its the ABS or the strange effect described causiong the reduced braking effect.
Any experiences / suggestions would be appreciated. The Norwegian dealer hasnt found any fault.
However a slight problem har surfaced and I wonder if anyone else has experienced the same thing:
When braking gently, after a very short period of retarding the car, the braking effect is markedly reduced in spite of constant pedal-pressure. (More or less like when the ABS engages on very icy surface. Applying more pressure to the pedal increases the braking effect, but particularly when driving on icy conditions this is annoying as you dont know or feel if its the ABS or the strange effect described causiong the reduced braking effect.
Any experiences / suggestions would be appreciated. The Norwegian dealer hasnt found any fault.
Rookie
Joined: Aug 2011
Posts: 72
Likes: 0
From: Missouri
I haven't driven my RX400h on snow or ice yet, but in the dry/wet, I haven't experienced anything like that.
However, with my IS-F, if I drive it into my garage with slush on the ground, the anti-lock brake system freaked out and the pedal went to the floor with no braking action. I had to use the e-brake to stop the car.
It was pretty scary at the time, especially the first time it happened!
Jeff
08 RX400h
However, with my IS-F, if I drive it into my garage with slush on the ground, the anti-lock brake system freaked out and the pedal went to the floor with no braking action. I had to use the e-brake to stop the car.
It was pretty scary at the time, especially the first time it happened!
Jeff
08 RX400h
Lead Lap
Joined: Jun 2009
Posts: 668
Likes: 11
From: Ontario
This is a known quirk of the hybrid system. What is happening is the system is using the electric motors for braking (regenerative braking). When you hit the icy patch and it decides a wheel is in imminent danger of locking up, it must switch from the regenerative braking (electric motors) to the tradionial brakes (calipers and rotors) due to the need for ABS.
In that split second of changeover, there is a period of reduced braking. Lexus/Toyota state it's normal, but it is disconcerting. You will also notice this same effect if you travel over a decent sized bump while braking. I think with bumps, the system thinks a wheel is locked up as the weight over the wheel hitting the bump is removed. It then transfers braking from the electric motors to the calipers and you notice a loss of braking just as you crest the bump.
More people have noticed this on bumps than ice. Once you get used to it, you'll find it easier to deal with. The key is not to panic and release the brake pedal, just brake as normal and let the system sort itself out.
I don't know why Toyota can't come up with a software flash to address this situation. Something as simple as keeping the regenerative braking engaged a bit longer until the regular brakes engage fully.
***By the way, you should probably post any hybrid specific questions in the Hybrid forum***
In that split second of changeover, there is a period of reduced braking. Lexus/Toyota state it's normal, but it is disconcerting. You will also notice this same effect if you travel over a decent sized bump while braking. I think with bumps, the system thinks a wheel is locked up as the weight over the wheel hitting the bump is removed. It then transfers braking from the electric motors to the calipers and you notice a loss of braking just as you crest the bump.
More people have noticed this on bumps than ice. Once you get used to it, you'll find it easier to deal with. The key is not to panic and release the brake pedal, just brake as normal and let the system sort itself out.
I don't know why Toyota can't come up with a software flash to address this situation. Something as simple as keeping the regenerative braking engaged a bit longer until the regular brakes engage fully.
***By the way, you should probably post any hybrid specific questions in the Hybrid forum***
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Driver
Joined: Mar 2011
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From: Prescott,Arizona
Now you mention it, I too have felt it once and even though it was not a panic situation, I wondered why. Tried to get it to do it again and could not. Now I know. Thanks for the first post on a very interesting topic.
Thread Starter
Driver School Candidate
Joined: Nov 2011
Posts: 7
Likes: 0
From: Outside US
Thanks for moving the thread. 
I appreciate that this has happened occasionally for some of you. For me its a daily occurrence.
The reduced braking effect is subtle but definately noticable, and the only thing you have to do is to increase the pressure on the pedal. The only problem is that it mimicks the effect and feeling you get when ABS is activated on icy roads. (We get that a lot in Norway) So when it happens you dont know for sure what is what and your instincts are tricked.
I appreciate that this has happened occasionally for some of you. For me its a daily occurrence.
The reduced braking effect is subtle but definately noticable, and the only thing you have to do is to increase the pressure on the pedal. The only problem is that it mimicks the effect and feeling you get when ABS is activated on icy roads. (We get that a lot in Norway) So when it happens you dont know for sure what is what and your instincts are tricked.
Pole Position
Joined: Sep 2006
Posts: 3,054
Likes: 103
From: Sacramento, California
I get a really strange sound somegtimes, sounds like a gurling and pop on my rx400h , definetely related to brakes, you hear it after pulling into garage and stopped before going into park....does anybody else get these weirrd noises?
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