Ok, just had my first braking "scare" in my 2016 Leaf this morning in the wet on the way to work.
There is a section of road that curves to a give way that has a huge rut all the way across the lane that is something like 20cm wide (thanks Glasgow city council...) which is pretty harsh to drive over at the best of times. It's a stretch of road on one of my "alternative" routes so I drive over it approximately 50% of the time on the way to work so I know it well.
This morning was very wet and I was going perhaps a little faster than usual, (although still under 30) and coming towards me the opposing road forks - I need to give way to cars taking the right fork but not the left fork and it's not always obvious until late which fork oncoming cars are going to take because nobody indicates.
So yeah, I got caught out a little and had to do some "firm" braking which unfortunately coincided almost perfectly with the front wheels hitting the rut. I then experienced what many people describe - almost complete loss of braking force for an extended period of time.
By instinct I immediately pressed down a lot further and harder and there was still some braking available, however it was very weak and felt completely unassisted causing me to come to a fairly leisurely stop, fortunately short of the give way line. It all happened so quickly that I had no time to think about pressing the foot operated parking brake as well, although if I had been stopping over a longer distance from a higher speed I would have had time to apply that too.
No warning lights came on and the loss of braking assistance I estimate lasted more than 2 seconds, (until after I had stopped in fact) with no discernible ABS "pulsing" just "bam!", loss of assistance the instant I hit the rut and assistance never came back until after I stopped. After I moved off the brakes were working normally again.
So what happened ? I know a fair bit about how braking and ABS systems work and have done troubleshooting on faulty systems before so of course I've been turning it over in my head trying to work out what happened, although this is made more difficult due to the Leaf's somewhat unique electric brake servo system.
One thing is clear - hitting the rut in the road was the instigating event which triggered the whole thing as the loss of brakes happened the instant I felt the rut hit.
It's not uncommon for ruts in the road to trigger ABS on cars - when the wheel falls into the rut it accelerates very quickly then when it climbs out it decelerates very quickly. If this deceleration coincides with you firmly applying the brakes this is interpreted as the wheel locking up and ABS will trigger on that wheel releasing the brake on that wheel. But usually this will only result in some pulsing that lasts maybe half a second or so, and only on the affected wheel. If you're riding the brake lightly its common to feel the pedal pulse on some cars when you pass a rut as the speed sensor detects the sudden increase and decrease in wheel speed.
There are some compounding factors here to make the situation worse though:
1) The Leaf like most EV's seems to cut regen completely the moment the ABS activates for any reason. If you're decelerating at a modest rate a lot of that is coming from regen so an instantaneous loss of regen when say 70% of your deceleration is coming from regen will feel like a momentary brake failure - you have to press the pedal a lot harder to bring in the friction brakes to restore the amount of deceleration you had prior to the regen being cut. I suspect this is what a lot of people having "mild" brake failures on their Leaf's are actually experiencing - just the sudden removal of regen, and I have experienced that several times on my previous EV (Peugeot Ion) as well.
2) There was a lot of rain and a bit of flooding this morning so it's likely the discs were wet and not working at their best and regen means that unless you brake hard there is not enough friction brake use to dry the brakes out properly - meaning that when regen was cut the friction brakes were probably not working nearly as well as they should be due to being wet, this would make the loss of braking feel even worse.
3) The rut is straight across the lane so both left and right wheels hit it simultaneously meaning ABS action is going to cut braking to both wheels on the same axle at the same time whereas ABS is normally designed to cut braking to individual wheels that are on slippery patches.
4) Although it's hard to be sure, I think ABS kicked in on the rear brakes when they hit the rut as well, and near simultaneous activation of both front and rear ABS is going to seriously limit your braking.
Even with all this there was some braking force available but it was weak and unassisted. If I was just experiencing ABS pulsing the brakes should have returned to full strength in a fraction of a second after the rut was passed so I suspect the main issue was the removal of regen for an extended period of time (regen is cut for much longer than a normal ABS pulse interval) and wet friction brakes that were ineffective under moderate braking.
And before anyone asks, yes my 2016 30kWh Leaf already has the brake control unit firmware update that supposedly fixes the "known" issues with the brake control unit. Also my 12v battery was replaced only a few weeks ago so weak 12v battery can be ruled out.
I can totally see how someone who doesn't understand how Braking/ABS/Regen systems work and interact with each other would see this as a "brake failure".
