My Leaf roll back and almost kill a kid!

[oscar]

Ok got the call today to pick up my car tomorrow. Their explanation was I got all these faulty errors was due to a 12V battery. They have all my error codes download and conclude the 12V cause the can bus to go hay wire. They replaced the 12V battery and drain my main battery and recharge. They said everything is working fine. I’ve ask them over the phone was there any cause from the mechanical brake. Their respond was 12V cause faulty error and no mechanical brake issue.

Also the 12V will solve the start issue on the uneven pavement. Guys don’t worry once I get my car back I know where to park to see if this problem is resolve.

For the record before I brought my car in for service. I did check the 12V battery every time I had issues in past. I measure with my voltmeter reading 10.7V to 11.2V.

Anyway I will continue to monitor my issues and update in 3 months. If I see no more issues; I can conclude the 12V battery replacement fix all my issues. I will also ask if they updated the software or kept the current version. Again Thanks to all that supported my issues and wanting Nissan to improve for future generation to enjoy the Leaf and safety come first!

 

[RegGuheert]

Great news!

They have all my error codes download and conclude the 12V cause the can bus to go hay wire.

CANbus flakiness was what I had predicted. As such, this sounds like a reasonable diagnosis.

For the record before I brought my car in for service. I did check the 12V battery every time I had issues in past. I measure with my voltmeter reading 10.7V to 11.2V.

That's too low. I agree it sounds like a shorted cell. Hopefully the voltage got well below 10.7V before the CANbus started misbehaving.

Anyway I will continue to monitor my issues and update in 3 months.

Please update before 3 months! Let us know if things are working properly after a couple of days.

Anyway, kudos to your Nissan dealer. It sounds like they did a good job with the diagnosis and repair!

 

[DaveinOlyWA]

10.2 volts on a 12 volt battery is "barely" this side of dead...very dead. surprised anything worked at all

 

[Nubo]

I hope someone can explain how a bad 12V battery can cause the brake pedal to suddenly go to the floor. Where is the brake fluid going from the displacement of the master cylinder? :?:

 

[DaveinOlyWA]

I hope someone can explain how a bad 12V battery can cause the brake pedal to suddenly go to the floor. Where is the brake fluid going from the displacement of the master cylinder? :?:

I can believe it. the initial pedal travel controls regen response.

now when pedal is depressed quickly the brake controller senses it and sends message to master cylinder to pressure up quicker. if pedal is depressed slowly, controller tells master cylinder to pressure up slower. this allows greater regen when an emergency or urgent braking response is not needed which would be most of the time.

either way, i still find it difficult that the car would even boot up with 12 volt batttery that low. in fact, it really should not happen. OP mentioned that sometimes he had to sit there for extended periods to start the car. is it because the 12 volt battery needed time to build enough voltage to boot the computer? wow...

 

[Smidge204]

But even with the power off and both batteries disconnected, the brakes will still work. Poorly, with no boost, but they'll work.

I'm really at a loss for how a power/computer error can allow the pedal to go all the way to the floor with no braking force.
=Smidge=

 

[RegGuheert]

I hope someone can explain how a bad 12V battery can cause the brake pedal to suddenly go to the floor. Where is the brake fluid going from the displacement of the master cylinder? :?:

This was not a "no power" situation. I agree there would be unassisted brake power in that case. But the antilock braking system has the ability to relieve pressure between the pedal and the wheel cylinders. If it were improperly commanded to do this, it would prevent the pedal from applying enough pressure to stop the car.

That's my best guess, anyway.

 

[DaveinOlyWA]

i also think we have to go back to the user. the difference in power assisted brakes W/WO power is pretty extreme. Its easy to see someone not prepared for the difference to be shocked at the difference in effort required to slow the vehicle.

been there, done that and ya, you gotta stand on em to stop. if the computer is not working correctly, it could be interpreting signals that there is little or no pedal acceleration and there is nothing more than a gentle call for deceleration and is thinking the regen is doing the work.

 

[aqn]

Personally, I would rule out mechanical or hydraulic issues in the brake system such as leaks or seal failure. If there were such issues, one would encounter brake performance problems more frequently than a random once in a while.

While there are no leaks, there are places the brake fluid in the master cylinder can go. For example, as RegGuheert pointed out, the ABS would bleed pressure off of the hydraulic circuit of the wheel that is locking up. A software bug would cause such a condition, causing all hydraulic pressure generated at the master cylinder to be bled off completely. That would account for the "pedal sinking to the floor" symptom.

A glance at the service manual, pages BRC-35, shows that the "ABS actuator" and the "electric unit (control unit)" (presumably the Brake Control Unit, this being the chapter on brakes) receive the following signals:

• Accelerator pedal position signal
• Motor torque control signal
• VCM control signal
• Shift position signal
• Electrically-driven intelligent brake control signal
• Steering angle sensor

To me, it's not far fetched that there is a software bug somewhere in interpreting/processing these signals, a "corner case" that requires unusual conditions or unusual combination of factors.

 

[Smidge204]

Personally, I would rule out mechanical or hydraulic issues in the brake system such as leaks or seal failure. If there were such issues, one would encounter brake performance problems more frequently than a random once in a while.

Not true. I used to drive a station wagon that has a faulty master cylinder, and maybe three times in two years I lost braking power. A bad seal can easily function 99% of the time without giving out entirely. It wasn't until the one incident resulted in a collision (very minor, no damage to either vehicle thankfully) that I did a tear-down of the entire system and found two bad seals in the master cylinder.

This was not a "no power" situation. I agree there would be unassisted brake power in that case. But the antilock braking system has the ability to relieve pressure between the pedal and the wheel cylinders. If it were improperly commanded to do this, it would prevent the pedal from applying enough pressure to stop the car.

The pedal would still not go soft, even if the ABS valves failed in the worst way possible, because while the valve is in "relief" mode it also blocks further fluid from leaving the master cylinder. The very notion that there is a possible scenario where an electrical/electronic fault can result in total brake failure is unforgivable, IMO.

i also think we have to go back to the user. the difference in power assisted brakes W/WO power is pretty extreme. Its easy to see someone not prepared for the difference to be shocked at the difference in effort required to slow the vehicle.

This point has a lot of merit to it...
=Smidge=

 

[kubel]

E-brake activation in emergency situations requires you to pull and hold, correct? (assuming there's 12V available to the ebrake)

 

[oscar]

12/02/2012
Pick up the car this morning. Once started the Leaf mileage reading show 105 miles on display. I’ve notice the brake felt different in a way that it felt stronger not relax feel as before. I drove the car home and measure the voltage and new battery reading 12.31 volts. Anyway I will do more testing on uneven pavement testing in next few days. Hope all my problem is resolve due to low 12V battery. If this is case we should all measure our 12V battery often….wow! Now I’m wondering what happen in real situation when the car let you start up and while driving the 12Volts battery is lost…does this mean you lost power to certain controls? I just hope we don’t lost power to our emergency brake…

"Report came back found multiple codes 62 total. The mechanic in charge called the Nissan Tech Line and had them review all but found all up to date. Tech Line confirms that 12V battery went low; recommendations from tech line replace new 12V battery (NB51R). Test drove and check for codes again. All to be ok".

 

[DaveinOlyWA]

12.3 volts on "new" battery? i think next thing to do is get your voltmeter checked. it probably needs batteries too

 

[abasile]

Considering the apparent safety implications, it seems to me that the car should warn the driver if the 12 V battery is fading, along the same lines as TPMS.

 

[DaveinOlyWA]

Considering the apparent safety implications, it seems to me that the car should warn the driver if the 12 V battery is fading, along the same lines as TPMS.

62 codes? i am guessing there was some warnings

 

[oscar]

Considering the apparent safety implications, it seems to me that the car should warn the driver if the 12 V battery is fading, along the same lines as TPMS.

62 codes? i am guessing there was some warnings

Most of these codes is a repeat. I had these problem for few months but never bothers bringing it in for service. The car sometime act up and let me start and at other time I had to wait 20 minutes. This happen to me more then a dozen time. What I regret most was I had to pump gas for my rental car $30 worth first time in 18 months!

 

[cwerdna]

Personally, I would rule out mechanical or hydraulic issues in the brake system such as leaks or seal failure. If there were such issues, one would encounter brake performance problems more frequently than a random once in a while.

Not true. I used to drive a station wagon that has a faulty master cylinder, and maybe three times in two years I lost braking power. A bad seal can easily function 99% of the time without giving out entirely. It wasn't until the one incident resulted in a collision (very minor, no damage to either vehicle thankfully) that I did a tear-down of the entire system and found two bad seals in the master cylinder.

On this note, I'm wondering about the braking on the Leaf. Is it like the Gen 2 Prius where the last few mph (say 5 mph or so) down to 0 is done solely by friction braking? I'd imagine that on the Leaf, if you slam on the brakes (at higher speeds) that it'll force the friction brakes to kick in as well, right?

Also, if you shift to neutral and use the brakes, is it relying solely on the friction brakes and there's no regen? That's the way it is on the Prius. If so, it'd be interesting for the OP to shift to neutral and test out his friction brakes to see if they stop reliably...

If my assumptions about the Leaf are true, then I'd imagine most people are getting most of their braking from regen and thus hydraulic brake problems may not be as easily noticed.

 

[mwalsh]

If my assumptions about the Leaf are true, then I'd imagine most people are getting most of their braking from regen and thus hydraulic brake problems may not be as easily noticed.

That's certainly true for me. It's become a bit of a game...trying to avoid use of the friction brakes at all.

 

[aqn]

This was not a "no power" situation. I agree there would be unassisted brake power in that case. But the antilock braking system has the ability to relieve pressure between the pedal and the wheel cylinders. If it were improperly commanded to do this, it would prevent the pedal from applying enough pressure to stop the car.

The pedal would still not go soft, even if the ABS valves failed in the worst way possible, because while the valve is in "relief" mode it also blocks further fluid from leaving the master cylinder.

Are you completely sure about this? That one ABS valve being in "relief mode" would "block further fluid from leaving the master cylinder"?

 

[planet4ever]

Also, if you shift to neutral and use the brakes, is it relying solely on the friction brakes and there's no regen? That's the way it is on the Prius.

Unlike a number of others here, I never use neutral while the car is moving. But the Owners Manual is very clear:

Starting and driving
. Driving vehicle
. . Electric shift control system
. . . Shifting
. . . . N (Neutral)
<snip>
The regenerative brake system does not operate in the N (Neutral) position. However, the vehicle brakes will still stop the car.

I will note that I carefully trimmed off the first sentence in that paragraph, since I didn't want to bias the pro-neutral folks against the part I quoted. :|

Ray