: Nissan Leaf

Information

The LEAF has conventional hydraulically operated friction brakes. Additionally, the LEAF’s electric motor provides regenerative braking.
The hydraulic brakes is electrically assisted. Nissan LEAF Service Manual, BR-10 – BR-13
An internal motor operates a piston in the master cylinder to generate assist force.
A brake pedal stroke sensor detects the amount of brake pedal operation and signals the “electrically-driven intelligent brake unit” (IBU).
The IBU performs cooperative control of the regenerative brake and friction brake according to brake pedal travel and amount of cooperative regenerative brake control.
A pressure sensor in the master cylinder informs the IBU which increases or decreases brake assist so pressure inside the master cylinder equals a “target pressure”, derived from amount of brake pedal movement.
Cars with internal combustion engine . Since the LEAF does not have an internal combustion engine, an electric pump provides additional hydraulic pressure and acts as the brake booster Nissan LEAF Service Manual, section BR, page BR-11.. In the event of power loss, a large capacitor (called a “brake power supply backup unit”) provides stored electricity to power the pump The Nissan LEAF service manual, page BR-11. The brake power is described on page BR-11 under “Brake Power Supply Backup Unit”. Its exploded view is on page BR-223..
Here is a pic of the capacitor (“brake power supply backup unit”):

Here is a pic of the Toyota Prius’ brake back-up power capacitor assembly:

• Pictorial tour of the LEAF’s brakes (and suspension), front and rear.
• The LEAF regens at up to a max of 30kW, versus the Gen 2 Prius’ 21kW.
• See also: Battery, Charging System.
• Diagram of the “electrically-driven intelligent brake unit”, from the LEAD Service Manual, colorized:
  

Parking/ Emergency Brake

Operation

• To apply the parking brake while stationery, step firmly on the brake pedal and pull up on the parking brake switch to engage the parking brake. Pull up twice to apply maximum parking brake forceNissan LEAF Owner’s Manual, page 5-16..
• To apply the parking brake while moving, pull up and hold the parking brake switch; when you release the parking brake switch, the parking brake will be released .
• The parking/emergency brake can be applied while driving: pull up and hold the electric parking brake switch (page 5-16 of the ). A chime will sound. When you release the parking brake switch, the parking brake will be released. While moving, the parking brake is applied at a lower force than when stationeryLEAF Service Manual, page PB-20..

How The Parking/ Emergency Brake Works

The parking/emergency brake system consists of two drum brakes, one on each rear hubThe diagrams in the service manual (page PB-87) shows two cables, one going to each side.. The rear service brake’s rotor resembles a hat (5). The “crown” of the hat serves as the drum brake’s (2) housing. The drum brakes’ shoes are actuated by cables.
An “equalizer” (5) rides on a threaded shaft (4) and tensions both brake cables. An electric motor (1), operating from the 12V batteryNissan LEAF’s Owner’s Manual, page 5-16. drives the shaft via a reduction gear (2) and a clutch (3). The electric motor operates on signals from the parking brake control module, which receives signals from the parking brake button via the CAN bus. The emergency release (6) turns the reduction gear which turns the shaft which de-tensions the brake cables.

Here are a couple of pics of the parking brake’s cabling: pic 1 pic 2.

Problems/issues

• Defective brake control module: Getting yellow brake warning light along with yellow master warning light, also throwing an undocumented code: problem was a defective brake control module: replaced.
• Parking brake actuator problem:
• Parking brake’s light flashes, and “Park” warning in dash flashes, and dash says “visit dealer”.
  Nissan specialists investigated. Remedy was replacement of “brake actuator”.

• Another “parking brake stuck, with ‘visit dealer’ warning” problem, which also turns out to be a brake actuator problem.
• “Parking brake actuator overheating” error code.

• Reports of not having any brake assist:

• On start-up, user felt/heard clicks in the brake. The first stop took considerable extra effort. Subsequent stops were OK.
• Same problem.
• If user lets go of the accelerator on level road, he would get 4 bars of re-gen immediately. User turned off the car and had to push extremely hard on brake pedal before the car could be turned on. User heard a clunk as he was driving.
• Multiple occurrences of a similar problem, as yet not readily reproducible: brake pedal feels spongy, with no resistance & hits bottom, with little or no stopping power.
• Grabby brakes: Nissan has released a Technical Bulletin to address this issue:
• Nissan Technical Bulletin NTB12-086: “2011 LEAF; Brake Pedal Feel Below 15 MPH”
  
• Reports of grabby brakes:

• The brakes “gets into this “grabby” mode, especially coming to a stop, where it’s damn near impossible to creep up a little without giving everyone whiplash.
  I noticed if you completely let off and get back on, it resets this behavior and they are much more ‘normal’.“.
• Grabby brakes
• Creeping along in traffic, brakes become grabby.
• “…more grabby than usual…“
• “…’grabby brakes’ a few times at very low speed…“
• “…sensitive and jerky feeling…“
• A procedure which appears to “reset” grabby brakes, albeit temporarily, as the problem eventually resurfaces.
• Brakes applied harder/longer than intended:
• Reports to NHTSA.
• Accounts:
• “I too have noticed the grabby brake problem. Most noticeable at parking lot speeds. I press the brake peddle just a little to slow the momentum of the car down. Instead the brakes grab and stop the car to complete stop. It does it quickly enough that you and anyone ridding in the car jerks forward.“
• Sudden braking leads to prolonged brake application even after pedal pressure is removed.
• “I had to slow down suddenly and I pressed hard on the brakes. I then let up on the brakes, but the car kept braking hard and the tires locked.“
• “…car in front of me stopped suddenly. I slammed on the brakes and pulled to the right to get some more space. I also pulsed the brake pedal to flash my rear brake lights for the guy behind me. Then the tires completely locked up for about half a second and then I kept on going.“
• “…continued to brake hard after the brake pedal was released for a 1/2 second or so…“
• Car slowing more than intended.
• “…stomped on the brake, activating the ABS. As soon as my front end was behind his bumper, I lifted my foot off the brake so as to avoid being hit from behind. But as others have experienced, the car continued to brake on it’s own until the Leaf came to a complete stop.“