Transmission B Mode -- Do my brake lights come on?

No, they do not.

 

is it bad if you accidentally leave it on B and drive for a few seconds? What is B exactly LOL!

 

The mechanical switch that activates the brake lights is activated by the
movement of the brake pedal arm. There is no mechanical or eletrical
connetion between the brake lighs and the "B" condition. As a result, the
brake lights are not illuminated when in "B."

This shouldn't be cause for alarm. With a manual transmission, and for an
automatic transmission for that matter, when you downshift to a lower
gear -- for example to not burn up your brake pads/shoes on a long
downhill descent -- the car slows down with no brake lights.

The decelleration experiened in "B" is much less than with a
manual/auto transmission downshift.

Drive on. Be happy.

 

B mode is "Brake" mode, which turns on engine braking. It is similar to downshifting a normal car, or using a jake brake on a diesel. B mode takes regenerated electricity from braking and dissipates it by spinning the engine as a big air pump. Its purpose is to deliberately waste energy to slow down the car while minimizing the use of friction brakes. About the only time you need to use B mode is descending long steep hills.

Tom

 

From my driving experiences....

I've used it on really really big hills >5 miles and noticed you might not hear the increase in noise for the first mile or so (guessing b/c the car is charging the traction battery before wasting.

I really like B mode, and I really don't worry about using the brakes "too much" even if not using B mode, because I figure the majority of the power is going back into the battery.

 

I've found after several trips in the mountains ouside Denver that the best way to control regen/engine braking is by using the cruise control on down hills. It starts with just regen unless it cannot keep the speed then it will add engine braking. When the battery is full it starts harder engine braking. The long 6%+ grades it can keep the speed to 65. I have seen 5045 rpm on engine braking, but i figure this should not be to bad on the engine or the cruise would kick out like it does on other vehicles i have.

 

No it won't hurt a thing if you forget and leave it in B. It will go back into D after a short time if you are just driving normally. You may notice anyway because the CC will not work in D.

 

Contray to your post, in my car I inadvertently left it in B after going down a long hill and it stayed in B for maybe 15 minutes until I noticed a loud sort of noise (like you get when driving too fast in a manual trans) when I hit about 65 mph. I figured if I screded something up it would have shown itself by now. Although I had been a little concerned about it..but hey , I have another 35000 plus miles left on the warranty!

 

Well, I believe there is an error in the explanation of "B" mode here. It doesn't -require- regen or electric generation to function. It uses electrical current to "stiffen" the magnetic fields in the MGs to cause the engine to spin and doesn't inject fuel. Thus it wastes energy by compressing air, causing a drag on the car. It -IS- about as effective as "downshifting" an automatic, at least on Pearl it is.
-AFTER- an episode of "B" braking you may find the battery is full, and -then- the HSD will try to dump energy from the battery by spinning the engine with MG2 (with no fuel injected). But only on long descents, say more than a few minutes.

Feel free to use "B" whenever you like, remembering that you ARE wasting energy. Now if that energy were to be wasted as heat in the brakes, fine, no difference.

One caveat. "B" mode brakes the front wheels only, just as regen braking does. In -some- situations that could be bad. Think glare ice. Swapping ends is not fun! -I- haven't noticed this problem, and have had lots of chances for it to happen, but it's possible. Be warned!

 

Only use B mode for going down long hills to avoid using mechanical brakes after the HVB is full. It does not help your traction in snowy/icy conditions. Use D and normal braking for that.

 

I think my answer may have been based on what I remember from my Gen2. I have to take a highway trip tomorrow I'll try driving 20 miles or so in B and see if it drops out. It's not really important but I'm curious now.

I think I know what the loud noise you heard may have been, I'll try to confirm that too. Mine is still under warranty also.

 

It won't be any more dangerous than downshifting a traditional manual or auto transmission FWD in the same conditions.

 

While B mode can occur without regeneration, this would be rare. To do this, power would be drawn from the traction battery to power the field windings of MG1.

Normally regenerative braking precedes engine braking, even when in B mode. This regenerative braking produces electrical energy which is normally used to recharge the traction battery. When engine braking comes into play, some or all of this regenerated energy is used to power the field windings of MG1. Depending on how much energy needs to be dissipated, the field in MG1 may exert only a slight drag, forcing the engine to turn slowly, or the field may power MG1 to force the engine to spin at a higher speed. It all depends on how much engine braking is needed, but in the general case at least some of the dissipated energy goes through an electrical path to the engine.

Tom

 

On ice and snow, the wheels break traction and start skidding. Same with a stick shift.

 

Modern automatic transmissions will ignore you if you try to downshift at too high a speed. They are fairly idiot resistant.

You can pull one into 2 or even L at 100 mph and it won't do anything until you get down to an acceptable speed, then it will downshift.