RX400H Light braking

welland · February 23, 2018

Over the last week or so, whilst using our RX400H for some longer trips, i have discovered that it is very difficult to brake lightly and smoothly. Under light braking, the car slows initially, but much of the time, there is a characteristic kind of snatching at the brakes. There is no such feedback through the brake pedal - only the feeling that the car is decelerating very rapidly. Is this a characteristic of the hybrid generstion system?Or is something wrong?

rayaans · February 23, 2018

6 minutes ago, welland said:

Over the last week or so, whilst using our RX400H for some longer trips, i have discovered that it is very difficult to brake lightly and smoothly. Under light braking, the car slows initially, but much of the time, there is a characteristic kind of snatching at the brakes. There is no such feedback through the brake pedal - only the feeling that the car is decelerating very rapidly. Is this a characteristic of the hybrid generstion system?Or is something wrong?

Sounds somewhat normal for the 400h which has an older regenerative braking system.

Common complaints are difficulty braking smoothly and difficulty in assessing how hard to brake, sometimes stopping quicker than expected and being 1m in front of a traffic light marking line for example.

Most people get used to it but yes, sometimes the brakes can be difficult to modulate in earlier hybrids

Having said that, if you've changed pads or discs recently, could be them - or brake fluid thats getting old.

sorcerer · February 23, 2018

Not necessarily just older cars, I think.

We've had an 05-plated RX300 for almost two years and as you know, we recently traded it in for a 63-plated RX450h. I was surprised by both the red Luxury at Lexus Bradford that I test drove and the black Advance that we actually ended up buying from Lexus Teeside, in that the braking systems on both cars are much keener and sharper than what we've been used to on the RX300 and, in fact, of any car that we've had in the last 15 years, so I'm assuming that it's just a characteristic of the regenerative braking systems.

Spacewagon52 · February 23, 2018

28 minutes ago, sorcerer said:

Not necessarily just older cars, I think.

We've had an 05-plated RX300 for almost two years and as you know, we recently traded it in for a 63-plated RX450h. I was surprised by both the red Luxury at Lexus Bradford that I test drove and the black Advance that we actually ended up buying from Lexus Teeside, in that the braking systems on both cars are much keener and sharper than what we've been used to on the RX300 and, in fact, of any car that we've had in the last 15 years, so I'm assuming that it's just a characteristic of the regenerative braking systems.

Not wishing to hihjack this thread but I hope you will do a review of your 450h when you have run it for a while. I found your posts on the RX 300 very informative, partricularly the mpg comparison, John.

sorcerer · February 23, 2018

1 hour ago, Spacewagon52 said:

Not wishing to hihjack this thread but I hope you will do a review of your 450h when you have run it for a while. I found your posts on the RX 300 very informative, partricularly the mpg comparison, John.

Cheers David, I'll certainly do my best my friend, but I can give you a very brief overview now - we absolutely love it!!

ColinBarber · February 24, 2018

I wouldn't say this is normal. I owned a 400h for 5 years and never had this issue and it is no worse than a RX450h or IS300h.

If you watch the power meter it will go down when you brake - this is the regenerative braking system doing the work. If you apply more pressure the needle will go no further and the extra braking is performed by the mechanical braking. You need to determine if you are experiencing the problem with just the regen braking, when mechanical braking is also being used, or at the transition point. One explanation is you have sticking callipers, which is common on the RX, and the mechanical brakes are grabbing when they start to apply.

welland · February 24, 2018

On 2/23/2018 at 4:57 PM, rayaans said:

Sounds somewhat normal for the 400h which has an older regenerative braking system.

Common complaints are difficulty braking smoothly and difficulty in assessing how hard to brake, sometimes stopping quicker than expected and being 1m in front of a traffic light marking line for example.

Most people get used to it but yes, sometimes the brakes can be difficult to modulate in earlier hybrids

Having said that, if you've changed pads or discs recently, could be them - or brake fluid thats getting old.

The characteristics you describe do sound familiar.... It is comforting to hear that others experience the same.

welland · February 24, 2018

12 hours ago, ColinBarber said:

I wouldn't say this is normal. I owned a 400h for 5 years and never had this issue and it is no worse than a RX450h or IS300h.

If you watch the power meter it will go down when you brake - this is the regenerative braking system doing the work. If you apply more pressure the needle will go no further and the extra braking is performed by the mechanical braking. You need to determine if you are experiencing the problem with just the regen braking, when mechanical braking is also being used, or at the transition point. One explanation is you have sticking callipers, which is common on the RX, and the mechanical brakes are grabbing when they start to apply.

OK. I've hardly looked at the power meter, but I'll try to take note of it from now on. Few questions about the regenerative braking:

1) When you say the power meter goes down, do you mean that it goes down below zero?

2) Under light braking, does regenerative braking happen even before the front brakes are employed? (Wondering if the sticking calipers could be just rear or front too?)

3) Is there a test mode that can be switched on that will temporarily disable regenerative braking in order to test the mechanical brakes?

rayaans · February 24, 2018

29 minutes ago, welland said:

OK. I've hardly looked at the power meter, but I'll try to take note of it from now on. Few questions about the regenerative braking:

1) When you say the power meter goes down, do you mean that it goes down below zero?

2) Under light braking, does regenerative braking happen even before the front brakes are employed? (Wondering if the sticking calipers could be just rear or front too?)

3) Is there a test mode that can be switched on that will temporarily disable regenerative braking in order to test the mechanical brakes?

It goes below 0 and into the blue bit when on regen. As it switches to mechanical brakes, it'll move back up to 0.

The regen kick in first in light braking unless at low speed. The mechanical brakes come on under heavy braking and just before the end of a stop.

You can test it by doing an emergency stop. It'll force the mechanical brakes to come on immediately

ColinBarber · February 25, 2018

10 hours ago, rayaans said:

It goes below 0 and into the blue bit when on regen. As it switches to mechanical brakes, it'll move back up to 0.

No, it will stay on maximum regen as both brakes will be operational at the same time. It will only go back to 0 if the batteries are overheating and cannot be charged.

rayaans · February 25, 2018

3 hours ago, ColinBarber said:

No, it will stay on maximum regen as both brakes will be operational at the same time. It will only go back to 0 if the batteries are overheating and cannot be charged.

Mine works differently - goes into charge when braking at first, then at the last stage of braking it goes back up to the mid point - or the 0 depending on which vehicle you have

ColinBarber · February 25, 2018

2 hours ago, rayaans said:

Mine works differently - goes into charge when braking at first, then at the last stage of braking it goes back up to the mid point - or the 0 depending on which vehicle you have

As speed slows, and the motor/generator turns less, the energy recovered will decrease and so the meter will start to return to 0. At around 5 mph the mechanical brakes do all the work so the power meter should be at 0 at that point.

rayaans · February 25, 2018

59 minutes ago, ColinBarber said:

As speed slows, and the motor/generator turns less, the energy recovered will decrease and so the meter will start to return to 0. At around 5 mph the mechanical brakes do all the work so the power meter should be at 0 at that point.

Yes, exactly, thats whats happening. At the end of the braking sequence, its almost always on 0.

welland · May 9, 2018

Hi All,

It's a while since my last post on this topic, so an update is long overdue. I've had plenty of time to observe the power meter and I have lots to report.

Just a quick recap of the symptoms:

Under light braking, the braking effect seems to oscillate between harder deceleration and lighter deceleration without making any adjustment to the force applied to the brake pedal. It feels like it would if I was pressing the brake, then releasing it, then applying it again, etc...., when really I am applying brakes with constant effort.

My observations of the power meter reveal that when the braking effect gets harder, the power meter dips down. When the braking effect diminishes, the power meter rises back to 0. Under prolonged light braking, the needle will dip for a second or so, then rise for a second or so. Then it will dip again, then rise again. Each time the needle dips, this corresponds to increased braking effect, and when the needle rises, the braking effect diminishes.

Some of you will remember that I have also been experiencing an intermittent problem with my Rear Motor Generator (MGR)and I wonder if this may be involved in my braking issue :

While driving with the system warning messages displayed, I think that the rear MGR may have stopped regenerating. At this time the brakes were perfectly smooth, and the oscillating hard / light braking did not happen. Also, the power meter never dipped below zero, but strangely, the infographics still showed that electricity was being regenerated under braking, and the energy meter still plotted the little squares on the bar chart. I wonder if this means that the rear generator generates more than the front generator?

When the fault with the MGR ws cleared, the braking issue returned to the way oit was before: oscilating braking effect, power needle dipping below zero, then back again, etc.....

I wonder if my experience sounds familiar to anybody? What do you all think?

ColinBarber · May 10, 2018

I'd say your braking experience is abnormal and may well be related to the warning you received. Something isn't working as it should.

Ala Larj · May 10, 2018

Not sure if this is relevant or related but I had a situation where I couldn't seem to stop smoothly and at low speeds it felt as if the brakes were juddering or the abs was kicking in. Thanks to the suggestion of another member on here I did a couple of heavy braking from high speed which solved the problem.

welland · May 11, 2018

11 hours ago, ColinBarber said:

I'd say your braking experience is abnormal and may well be related to the warning you received. Something isn't working as it should.

Thanks Colin.

The challenge, as ever, is how to identify the cause!

welland · January 17, 2019

Hi All,

My braking issue has been solved YAY. Brakes are perfect now, and I'm regenerating a LOT more than before (many more blocks on the power graph).

That's the good news. The bad news is that work was done on several components at the same time, so I can't be specific about which ones were the cause of the issue. I'll describe what was done, so you have some pointers of things to check if you have similar symptoms.

1) New rear pads and disks. I don't believe this was the cause of the problem, as the old discs actually had quite smooth surfaces. They were replaced due to excessive corrosion.

2) Front calipers both had one stuck slide pin. To solve it required replacement hangers, which I got from a breakers. It's possible this was a cause of the issue.
3) My left front driveshaft had a split ABS reluctor ring. Corrosion beneath the ring had expanded and forced the ring to snap. This was solved by fitting a replacement driveshaft obtained from a breakers. Prior to replacement, I did occasionally notice the ABS warning light flash under light braking on dry roads with good surfaces (ie no chance that skidding had occurred).

Hope this helps someone.

Jim Blake · December 16, 2023

Hi. I have a 2006 400H from new which up to recently has run beautifully. The problem now is sometimes It feels as if my brakes engage slightly mostly on long journeys causing the car to not run smoothly for maybe 5 mins and then seems to release and run smoothly again. The mechanic couldn't identify the problem and it was identified in an NCT (MOT). The back brakes were replaced with calipers which solved the problem initially but has now come back. Any thoughts .

ColinBarber · December 16, 2023

1 hour ago, Jim Blake said:

The back brakes were replaced with calipers which solved the problem initially but has now come back.

What was the time period between having the brakes replaced and the problem reoccurring?

Greisingel · December 17, 2023

Check your calipers. I occasionally strip the brake housing – ensure high quality pads and rotors (and check they are not warped). Ensure the sliders are clean and correctly greased. (Just getting the basics right).

It is true that the 400 has some slightly peculiar braking tendencies. One such is the sudden seeming and unwanted release of the brake while you are depressing to slow. It is momentary but slightly unnerving when coming up to someone's trunk. You get used to it.