Significantly reduced regen when braking

This isn't happening consistently, but it's happened 3 times in the past week, never before that.

When I'm braking moderately (enough to only partially engage the friction brakes), normally the regen maxes out, or gets close if my speed is low. Sometimes, the regen cuts out almost completely, and goes to 1 dot. This is most noticeable because the car makes a sudden decrease in stopping power, and almost feels like it's jumping forward.

This isn't so much a concern in lost efficiency, as it is I'm worried something might be malfunctioning. It doesn't happen enough that I can reproduce it, so it might be difficult for a tech to diagnose.

2014 SL
2000mi
Temperate Bay Area, CA
60-80% SOC when it occurs, so not because battery is full

Checking LeafSpy, it looks like nearly all of the shunts are active. ~80/96 bars are red. Not sure why, or what this means.

mctom987 said:

the car makes a sudden decrease in stopping power, and almost feels like it's jumping forward.

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Sounds like a malfunction to me. If regen is disabled it is usually disabled from the start of the trip and slowly increases. If it is cutting out mid brake, something is wrong.

mctom987 said:

This isn't happening consistently, but it's happened 3 times in the past week, never before that.

When I'm braking moderately (enough to only partially engage the friction brakes), normally the regen maxes out, or gets close if my speed is low. Sometimes, the regen cuts out almost completely, and goes to 1 dot. This is most noticeable because the car makes a sudden decrease in stopping power, and almost feels like it's jumping forward.

This isn't so much a concern in lost efficiency, as it is I'm worried something might be malfunctioning. It doesn't happen enough that I can reproduce it, so it might be difficult for a tech to diagnose.

2014 SL
2000mi
Temperate Bay Area, CA
60-80% SOC when it occurs, so not because battery is full

Checking LeafSpy, it looks like nearly all of the shunts are active. ~80/96 bars are red. Not sure why, or what this means.

Click to expand...

this happens after recharging your battery to 100%?

Upon hitting a bump in the road and/or encountering loss of traction, regen sometimes drops substantially. I'm not sure if this is what you are describing. However, when this happens, I let up on the brakes if possible, then re-apply the brakes to get regen back.

Edy said:

this happens after recharging your battery to 100%?

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Did you even read my post, or just the subject?

abasile said:

Upon hitting a bump in the road and/or encountering loss of traction, regen sometimes drops substantially. I'm not sure if this is what you are describing. However, when this happens, I let up on the brakes if possible, then re-apply the brakes to get regen back.

Click to expand...

This would be ABS kicking in. Regen disengages to allow ABS to maximize stopping power.
I don't think this is the case though, but it might be related. ABS makes a pretty distinctive sound and feel, that I'm not noticing.

I usually don't have time to repress the brake, as that's usually why I pressed it in the first place. I generally avoid braking except when necessary. Unfortunately, CarWings/Nissan rates this as very inefficient driving… but that's another subject.

mctom987 said:

abasile said:

Upon hitting a bump in the road and/or encountering loss of traction, regen sometimes drops substantially. I'm not sure if this is what you are describing. However, when this happens, I let up on the brakes if possible, then re-apply the brakes to get regen back.

Click to expand...

This would be ABS kicking in. Regen disengages to allow ABS to maximize stopping power.
I don't think this is the case though, but it might be related. ABS makes a pretty distinctive sound and feel, that I'm not noticing.

I usually don't have time to repress the brake, as that's usually why I pressed it in the first place. I generally avoid braking except when necessary. ...

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This sounds like the well recognized safety deficiency the LEAF has with losing braking when going over a change in surface condition.
I don't think it is related to ABS activation as the five times or so I have experienced in 38 months it was in low speed traffic when crossing man hole cover or railroad track.
It is like all braking not just regenerative is lost for about 0.3 seconds.
More likely a glitch in the traction control system or programming.
The brakes do reactivate but it can seem like forever when you're about to hit someone.
Nissan needs to diagnose and resolve this safety deficiency sooner rather than later with NHTSTA involvement. :shock:

Yep, that is my guess. The ABS in the Leaf is very aggressive - too much so IMHO - and if something triggers it, regen will drop to next to nothing.

abasile said:

Upon hitting a bump in the road and/or encountering loss of traction, regen sometimes drops substantially.

Click to expand...

Sounds like it just might be the ABS being a little oversensitive. I suppose it's probably better than the other extreme, and failing to engage when needed.

It hasn't been a major problem, I was just more concerned about it being a problem in the future. After all, something failing in the braking system is not something you should just assume is fine…

mctom987 said:

Sounds like it just might be the ABS being a little oversensitive. I suppose it's probably better than the other extreme, and failing to engage when needed.

It hasn't been a major problem, I was just more concerned about it being a problem in the future. After all, something failing in the braking system is not something you should just assume is fine…

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ABS / traction control has to be tuned just right.
Either over responsive or under responsive creates accident risk.

Just look back 30 years to the Audi unintended acceleration problem. I had another German manufactured vehicle and experienced it once in a drive through. Bad throttle position sensor caused engine RPM to very quickly jump from 500 to 1200. Only takes a moment of driver inattention or incorrect pedal use to have very bad response.

All LEAF driver's need to be cautious about the short loss of braking with a change in surface.

mctom987 said:

abasile said:

Upon hitting a bump in the road and/or encountering loss of traction, regen sometimes drops substantially.

Click to expand...

This would be ABS kicking in. Regen disengages to allow ABS to maximize stopping power.
I don't think this is the case though, but it might be related. ABS makes a pretty distinctive sound and feel, that I'm not noticing.

Click to expand...

This happens to me a lot on Pittsburgh's bumpy streets.
While braking, I'll hit a bad bump, or one of those metal bridge expansion joints (slippery in rain or snow). It's enough for the Leaf to stop regenning, but not bad enough (or perhaps not long enough) for the ABS to engage enough for me to feel or hear anything. And so it just keeps braking normally after that, but without regen, until I let up on the brakes & re-apply.

The same thing happens in my 2nd and 3rd gen prii. I don't think it's so much a design flaw in the leaf, or in setting overly sensitive ABS. I would assume if it's been there in cars with re gen braking as far back as 06 and not fixed with a major redesign that it is a limit of regen braking that the engineers are considering.

The 06 has almost 100miles and it needs shocks now. It has behaves differently now with worn shocks because when you lose the traction and you had mild regen it feels like you suddenly loose all braking, almost like you start accelerating with your foot lightly on the brake. I could see (and yes this is just an opinion) that an engineer might want to develop a system where the brakes reduce regen with mild bumps (not enough to trigger ABS with good shocks). This would prompt the driver to push the brake a little harder and thus activate the friction brakes. This could avoid a situation that that mild bump with worn shocks causes a lose of all traction and all regen brakes.

My second theory is that ABS cannot work as designed with regen braking (or with full regen) so when it senses a bump that comes close to needing the abs to kick in it first reduces the regen so that if ABS is needed there is no delay.

minispeed said:

My second theory is that ABS cannot work as designed with regen braking

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I'll guarantee that this is the issue. They already have working ABS designed for friction brakes, and it's not designed to work alongside electric regen. So when the ABS kicks in, regen is disabled. Just a simple expediency in development.

At some time in the future, I expect a manufacturer will design an ABS system that interacts well with regen - perhaps even by using regen in addition to friction brakes to slow the vehicle. Then they will all start to follow suite.

it may be in relation to the "Grabby brake" syndrome. Even though it was fixed it still happens - sometimes you just press it slightly hard enough (just barely) and the car quickly breaks hard. Its annoying at best.

In light of this discussion, it's easy to guess why Tesla's engineers opted to not provide regen when the brake pedal is pressed. Tesla regen is controlled entirely on the accelerator pedal, and there is substantial regen if that pedal is fully released. This eliminated a whole set of engineering challenges.

abasile said:

In light of this discussion, it's easy to guess why Tesla's engineers opted to not provide regen when the brake pedal is pressed. Tesla regen is controlled entirely on the accelerator pedal, and there is substantial regen if that pedal is fully released. This eliminated a whole set of engineering challenges.

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This is what I want in B mode…

This is also the most ICE-like behavior, too. But that has nothing to do with why I want it.