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Poor braking effect using the "B" option on the gear selector


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I had a new model Yaris as a loan car earlier this week - only 180 miles on the clock.  I used the "B" option frequently on it and was amazed at how effective it was - certainly much, much better than on my 2015 Auris!

This promped me to wonder why and could my Auris's poor braking performance using the "B" option be improved?  I know nothing about how CVT transmissions work but it's surely not a matter of an adjustment somewhere or a worn part in the gearbox. Or is it?

Any thoughts?

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In what circumstances were you using "B" mode????

Our 2010 Auris Hybrid Owners Manual states "B - Applying moderate engine braking when driving down hills or on steep slopes".

My 2016 Prius Owners Manual states "B - Applying engine braking or strong braking when the accelerator pedal has been released on steep downward slopes etc".

SO, clearly, MR T is saying B mode is for a braking aid when travelling down steep hills/slopes.  I have rarely used the B mode, and even when I have when the hills have been so steep, in parts I have had to exert heavier foot pressure on the vehicle brake pedal.  If you constantly feel you need extra braking effect, then perhaps driving style needs to be looked at ie too fast, too close to others, braking too late.

B mode is an aid, but not a relacement for diver being in control of the vehicle.  As far as I know B mode is not adjustable.

So what does your Auris Owners Manual state re B mode????

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Hi, 

B mode is an engine braking and not to be used often as per the manual. Since the cars are hybrid and have two engines ice and e motor when driving in town at low speeds the engine braking happens entirely from the e motor as ice is off, when car moves at higher speeds and B is selected the ice will even start to deliver extra engine braking if been off prior to your B selection. The difference between two cars can be for various reasons, most common IMO is at software level , higher regenerative power ., something that driver can not control on either of the vehicles. The only time when you can have poor regenerative braking due to a fault with the car will eventually be when your car is at 300+k miles and the compression of the ice is lower due to wear in the cylinders. I don’t think there is anything to worry about, these are two different cars from two different generations of hybrid technology and although they are very similar, finding difference between is normal. B mode actually does not help much with efficiency and add extra stress to the hybrid system, better not to be used frequently., free rolling is the key to higher mpg. 👍

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I was using B mode as an extra set of brakes, if you will.  I was not driving with B mode on all the time and only selecting it when I would have applied the brakes anyway.  But I will bow to Joe's and Tony's advice and only use B mode when downhilling!

Thnks for your advice.

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Don't forget "B" is "Boost" and is to give additional charging to the Hybrid Battery when the car is coasting down hill or slowing down with the foot off the throttle. The fact that is gives some additional braking is only because it is driving a generator/motor to charge the Battery, it is not really designed as a braking system in itself.

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6 hours ago, Geoff P said:

Don't forget "B" is "Boost" and is to give additional charging to the Hybrid battery when the car is coasting down hill or slowing down with the foot off the throttle. The fact that is gives some additional braking is only because it is driving a generator/motor to charge the battery, it is not really designed as a braking system in itself.

Geoff, can you tell us what your Auris Owners manual says about B ???

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13 hours ago, Geoff P said:

Don't forget "B" is "Boost"

Where did you hear that?  It actually is Brake.

Reinforcing what Catlover and Tony HSD have already said, I'll add the folllowing.

13 hours ago, Geoff P said:

is to give additional charging to the Hybrid battery when the car is coasting down hill or slowing down with the foot off the throttle.

While the second part of your statement is correct, the first part is actually the opposite of what happens.

The idea of B is to reduce the amount of charge into the Battery so it takes longer to fill going down steep grades.  The extra braking come from the engine (ICE) being reconfigured to provide a higher level of engine braking.  I would only use B for any grade descent where the Battery was not totally full before reaching the bottom.  I can't think of anywhere in the UK that is steep or long enough where you would need use it.

This brings up another point.  One uses a technique when driving Toyota hybrid that goes against conventional driving wisdom, and that is using your brakes (i. e. the brake pedal) or 'riding your brakes', as it is conventionally called, while going downhill.  You can do this because a Toyota hybrid does not actually engage the hydraulic brakes (until quite a lot of pressure is applied or an emergency stop is initiated) but just increases regenerative braking therefore, there is no risk of overheating the pads and disks.  The power of the regenerative brakes is a lot stronger than most people imagine.

The second use of the brake pedal is to use it in place of where you would normally change down in a manual to slow for a stop ahead.  So you start your actual pedal press a lot further out than you would in a manual.  Try this one also and see your Battery fill.

To those that use the 'B' position, stop doing that for a few tanks and see how it affects your MPG as you try the above alternate techniques.

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The use of the 'B' position seems to be one of the most consistently misunderstood features of Toyota hybrids, and I wonder if that is partly behind Toyota's decision to 'hide' it on the latest 2.0 models?

Generally speaking in normal driving you should never select 'B' at all. It is there for use in potential emergency situations, for example when descending a steep mountain pass and the conventional hydraulic brakes overheat and begin to suffer from brake fade, or for extra control when driving in very severe snow.

A very common misconception is that using 'B' somehow puts extra charge into the Battery, or improves fuel economy. It actually does the opposite! It forces the transmission to engage the non-running petrol engine as basically a crude way of giving engine braking and slow the car. Using 'B' will put less charge into the traction Battery, not more.

Don't overthink it, and don't use B. Just press the brake pedal to slow down and the car will work out the most efficient mix of friction and regenerative braking for you.

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While I agree with most of what you have said I do not quite agree with this part:

27 minutes ago, yossarian247 said:

It is there for use in potential emergency situations, for example when descending a steep mountain pass and the conventional hydraulic brakes overheat

I don't know it something has changed in later models of hybrids, but in the earlier models it is not a mechanism for emergency use.  It was most definitely implemented to prevent exactly the situation you described except as a preemptive tool rather than a reactive emergency measure.  By engaging "B" in a descent it allows you to keep the car from running away without applying the brakes, or using very little of the brakes thus avoiding brake fade as a result of overheating.

Out of interest, how is this feature hidden in later models?

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5 minutes ago, Joseph D said:

While I agree with most of what you have said I do not quite agree with this part:

I don't know it something has changed in later models of hybrids, but in the earlier models it is not a mechanism for emergency use.  It was most definitely implemented to prevent exactly the situation you described except as a preemptive tool rather than a reactive emergency measure.  By engaging "B" in a descent it allows you to keep the car from running away without applying the brakes, or using very little of the brakes thus avoiding brake fade as a result of overheating.

Out of interest, how is this feature hidden in later models?

Yes I agree, bad choice of wording by me.

 

The subject came up on the C-HR forum recently. On the 2.0 hybrids there is apparently no longer a 'B' position on the transmission selector at all. They now have a feature on the steering wheel controls to adjust the gear ratio as described here:

 

https://www.toyotaownersclub.com/forums/topic/199046-no-b-setting-in-2-litre-c-hr/?do=findComment&comment=1568090

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Nick, the misunderstanding about B was prevalent way before the “latest 2.0 litre” models were for sale.

The misunderstanding should not be. I have two completely different Toyota hybrid cars, 2010 Auris and Prius Gen4, and two different Operators Manual. I have already stated what each manual says about the use of B and basically both read the same. Like a lot of queries, today “we” tend to use forums to get answers, whereas if first we referred to the manufacturers manual we would get a “true” answer, and not one passed from one to another and very often inaccurate. Toyota are clear on when B should be used, just follow the manufacturer and you are “on the right road”.

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B mode indeed is used for engine braking and extra Battery charge as a result of the first event since  the hybrid Battery power comes primarily from regenerative braking. B mode it’s not there to prevent any possible brake fade as this is almost impossible in normal driving conditions, the e motors slow down the car. Also B mode can operate without need of internal combustion engine to work in slow speeds in town driving, then in that circumstance the car behaves like a full ev with extra regenerative braking set, however there is drawbacks as driving in B mode kills the free rolling which actually helps the most with greater efficiency. Reading the car manual is the best advice IMO and then just experimenting, this is what I do and helps me understand the things how they work. 👌🚗👍

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2 hours ago, TonyHSD said:

B mode it’s not there to prevent any possible brake fade as this is almost impossible in normal driving conditions, the e motors slow down the car

In the absence of the "B" mode going down a long descent there would be brake fade, and especially if the Battery become full.  With nowhere to put the energy being generated, the only option would be the hydraulic brakes.  That is why the "B" mode exists.

2 hours ago, TonyHSD said:

Also B mode can operate without need of internal combustion engine to work in slow speeds in town driving

The engine and electric motors are always operating working together in synergy.  When you are using "B" mode the engine will be involved.  You just might not be aware of it because in town or other slow speed scenarios you will not necessarily hear it and you will not see it on the displays as it will not be fuelled.

But the important question is, why would you even be using it in that scenario?

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First - who told me it stands for "Boost". Answer Toyota Main Dealer.

Secondly I always use B when going down hill if the car is coasting and I usually have a full Hybrid Battery afterwards.

Eg: Brassknocker Hill in Bath,

Winsley Hill between Bradford on Avon and Bath

Sally in the Woods Hill again between BOA and Bath.

And one or two others.

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I find B mode a neat feature,because I know the hill is coming up,try to crest at the speed I want to go down,B ,holds me at 40 creeping up to 50mph then just a dab,is enough. Remembering to disengage,is the tricky bit.

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Something I've just remembered about my use of the Yaris loan car (see opening post).  When I switched off the engine I was given a brief resume about my driving and how I could achieve better mpg.  It never said anything about using B mode incorrectly!

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29 minutes ago, BigRedSwitch said:

Something I've just remembered about my use of the Yaris loan car (see opening post).  When I switched off the engine I was given a brief resume about my driving and how I could achieve better mpg.  It never said anything about using B mode incorrectly!

But seems like they didn’t mention B mode use to achieve better mpg.

So, when you asked “what is B used for”? What was you told?

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On 4/19/2021 at 10:34 AM, Catlover said:

So, when you asked “what is B used for”? What was you told?

I didn't ask.

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