Lost braking 3 times in the past 5 months on my 2015 Leaf!

[Nubo]

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How could a car braking system be designed in a way that the smallest variation in 12v battery charge would have a catastrophic failure of the brakes with zero warning? There are dozens and dozens of reports of the same failure all over the net, I'm just surprised that no recall has been issued yet. Are they waiting for fatal accident to happen? Do they really expect all the leaf drivers to trickle charge their 12v battery every single night?

That does not make any sense to me.

It's possible that the paradox could still be explained by a weak battery that is not revealing itself on a voltmeter check.

Resting voltage is not conclusive proof of a healthy battery. A load test is more definitive. I had similar problems crop up when one of my batteries developed a problem. Resting voltage was nominal, but I had repeated episodes where the dash would light up like a christmas tree. I finally put a load on the battery and the voltage dropped like a rock, which caused no end of trouble for the LEAF systems during power-up, including sketchy braking behaviors. All was fixed by a new, healthy battery and clearing the many DTCs.

This doesn't mean that your trouble is the 12V battery but I'd say it's worthwhile to get the 12V load-tested. Some parts stores will do this for free, or you can purchase a load-tester fairly cheaply. I now consider it good practice to load-test a lead-acid battery periodically to keep tabs on its health.

[SageBrush]

I now consider it good practice to load-test a lead-acid battery periodically to keep tabs on its health.

I think this is good advice. The last time I played around with this, I thought I would add a somewhat known load to the 12v for an hour or so and then check the 12v voltage. The obvious choice was the headlights, but the car would turn them off when the DC-DC converter was open.

Is there a way to do this ? I think I am asking how to enter ACC mode. I thought it was POWER button without holding down the brake pedal but my recollection is that did not work as intended, meaning the lights turned off after a few short minutes.

^^ This is all from memory, so I might be way off-base.

[knightmb]

I now consider it good practice to load-test a lead-acid battery periodically to keep tabs on its health.

I think this is good advice. The last time I played around with this, I thought I would add a somewhat known load to the 12v for an hour or so and then check the 12v voltage. The obvious choice was the headlights, but the car would turn them off when the DC-DC converter was open.

Is there a way to do this ? I think I am asking how to enter ACC mode. I thought it was POWER button without holding down the brake pedal but my recollection is that did not work as intended, meaning the lights turned off after a few short minutes.

^^ This is all from memory, so I might be way off-base.

It's changed between the Gen 1 and Gen 2. In the Gen 1, ACC mode would run for 15 (30?) minutes and shutdown automatically. ACC + On Mode (not sure what to call it, you press the power button twice while NOT holding the brake pedal to enter this mode) works differently now. On the Gen 1 Models, this *second* mode would run forever and if the 12V battery voltage got low enough, it would switch on the DC to DC converter from the main battery pack and then power everything (or charge the 12V also) until you shut it off. On the Gen 2, this *second* mode also shuts off after 15 minutes automatically (if not plugged in and charging).
The Gen 1 can kill the 12V battery in ACC mode, I've tested it myself.
In the ACC + On mode, the Gen 1 will try to charge the 12V battery once it reaches 10.5 V by switching on the main battery with the DC to DC converter. If the battery is too depleted to do this at 10.5V, the whole thing dies, again tested this one myself.
The Gen 2, using ACC + On mode, if the battery voltage gets down to 10.5 volts, it just shuts off like you powered it off. Either that or the battery died but did not cause a DTC code, I'm not really sure about that on my Gen 2s yet...

[Stanton]

I'm not 100% convinced this is a 12v battery problem...but if it is, I have an excellent solution for monitoring your 12v battery: the Anti-Gravity Battery Tracker (https://antigravitybatteries.com/produc ... lead-acid/). I used one of these (albeit the Lithium version) before I installed my OVMS module (which also tracks 12v battery behavior). The Battery Tracker also has some diagnostic modes that may be helpful...and it's not all that expensive.

[ctesti]

I'm not 100% convinced this is a 12v battery problem...but if it is, I have an excellent solution for monitoring your 12v battery: the Anti-Gravity Battery Tracker (https://antigravitybatteries.com/produc ... lead-acid/). I used one of these (albeit the Lithium version) before I installed my OVMS module (which also tracks 12v battery behavior). The Battery Tracker also has some diagnostic modes that may be helpful...and it's not all that expensive.

Thanks for sharing! Nice battery monitor.

I don't buy the battery problem: the battery was replaced twice in 5 months by the dealer, and the last one is only 5 days old and shows full charge. I would think the dealer would have done proper testing of the batteries before installing knowing that the problem they diagnosed was a battery issue!

Also the fact that the problem "heals" itself without doing anything would go against the battery theory. Every single time I had the problem, the orange and red light disappeared and braking came back by the time the car was towed to Nissan.

Same thing happened 2 days ago: no braking, battery 12.70v, everything else working fine, yellow and red warning sign on. 3 hours latter on the driveway no more warning lights and brakes woking as usual. Today the car was driving like nothing ever happened. DTCs still showing through.

Because the problem is happening more and more frequently, to me that would suggest another component is failing. I just wish it would be a total failure and be done with it.

[GerryAZ]

The error codes listed in the original post are all related to CAN bus errors. A low 12V battery can cause CAN bus communication errors, but I doubt that the 12V battery is the issue in this case since 2 replacements have been tried. Intermittent failures of control modules can also cause CAN bus errors. My 2015 had intermittent failures similar to what has been described here. The hydraulic brakes would always work without power assist, but the pedal would go almost to the floor and be very firm so it could feel like the pedal was going to the floor. Also, the ABS and/or intelligent brake controller would make incredible noise when the brake pedal was pressed.

I was always able to clear error codes and restore normal operation (often required disconnecting/reconnecting the 12V battery once or twice in addition to using Leaf Spy to clear the codes). The intermittent issue happened more frequently as mileage and time increased. Since I had an extended warranty, I eventually took it to the dealer when it happened at a time that was convenient to take it in. The dealer diagnosis was a bad intelligent brake controller. The replacement cost was about $3000 for parts and labor. I would have continued to clear codes and drive the car without replacing the controller if it was not covered by extended warranty.

[ctesti]

The error codes listed in the original post are all related to CAN bus errors. A low 12V battery can cause CAN bus communication errors, but I doubt that the 12V battery is the issue in this case since 2 replacements have been tried. Intermittent failures of control modules can also cause CAN bus errors. My 2015 had intermittent failures similar to what has been described here. The hydraulic brakes would always work without power assist, but the pedal would go almost to the floor and be very firm so it could feel like the pedal was going to the floor. Also, the ABS and/or intelligent brake controller would make incredible noise when the brake pedal was pressed.

I was always able to clear error codes and restore normal operation (often required disconnecting/reconnecting the 12V battery once or twice in addition to using Leaf Spy to clear the codes). The intermittent issue happened more frequently as mileage and time increased. Since I had an extended warranty, I eventually took it to the dealer when it happened at a time that was convenient to take it in. The dealer diagnosis was a bad intelligent brake controller. The replacement cost was about $3000 for parts and labor. I would have continued to clear codes and drive the car without replacing the controller if it was not covered by extended warranty.

Wow, thank you so much Gerry! That's exactly what's happening to me.
I also have an extended warranty, and the car is now at the dealer. They asked some help from Nissan engineers to diagnose the DTCs, I bet I have a similar faulty intelligent brake controller. I should have an update from them tomorrow...

[cwerdna]

GerryAZ: Ouch! Hopefully you'd filed a safety complaint w/NHTSA at www.safercar.gov. Might help others to do so, if you haven't already.

ctesti: Might help to do the same if that ends up being the fix for you too.

[GerryAZ]

GerryAZ: Ouch! Hopefully you'd filed a safety complaint w/NHTSA at www.safercar.gov. Might help others to do so, if you haven't already.

ctesti: Might help to do the same if that ends up being the fix for you too.

The brakes still worked (without power assist) so I saw no reason to file a safety complaint. I posted this issue in several other threads over the years that mention loss of brakes. Again, I always had braking capability although the pedal effort was high when the CAN bus communication failed.

[ctesti]

GerryAZ: Ouch! Hopefully you'd filed a safety complaint w/NHTSA at www.safercar.gov. Might help others to do so, if you haven't already.

ctesti: Might help to do the same if that ends up being the fix for you too.

The brakes still worked (without power assist) so I saw no reason to file a safety complaint. I posted this issue in several other threads over the years that mention loss of brakes. Again, I always had braking capability although the pedal effort was high when the CAN bus communication failed.

I filed a complaint with NHTSA each time I had the car towed to the dealer. The first time my wife lost brake assist, she panicked and had to call 911 since it was on a busy street. When the problem happened while I was driving, I also thought I lost all braking. It's only after reading some posts here in the forum that I realized I could press extremely hard on the pedal, ignore all the weird sounds and red orange light warning and eventually get the car to brake.

However I agree with cwerdna, for most drivers they'll believe they lost all braking, that's what my wife and I thought. This could end up with a deadly accident if it happens on a highway or busy street at a red light for instance.

So I agree that filing a NHTSA could be very helpful, potentially even safe lives. These intelligent brake control modules might have a factory defect and they might start going bad after 5 or so years...