Same Issue - Epilog
2013 JX35. Same situation with brakes.
1. Pedal intermittently loses pressure when slow speed stops.
2. Pedal goes close to floor at complete stop with light pressure.
3. On several occasions, it triggered the seat belt restraints which was scary.
4. Noted "air sucking" sound from brake pedal. Sounds like "Tin Man" gasping for air.
5. Brakes would "pump back" to normal if I took my foot off brake and repressed.
Car had just over 60K miles. Front and Rear brakes were replaced by dealership about 10K miles ago, no problems there. Brakes lines, caliper seals, obvious stuff checked out clean. But...there was definitely a leak somewhere in the system, just nothing obvious.
Went back to dealership. First attempt at repair resulted in Master Cylinder replacement. Seemed to be OK for 2-3 days. After that, same behavior and noise from pedal.
Second time back, they kept car for a couple days. Ultimately told me that problem was narrowed down to internal leak inside ABS Actuator. No codes just internal leak. They could physically hear a "hissing" sound. They replaced the part.
Service manager took car and drove it himself around for 2 days. Told him I wouldn't put my family back into car unless he would put his!
So far, no noise from brake pedal and brakes again feel firm with low speed stops. We'll see how things go for the next 30 days.
The Infiniti Dealership in Maryland (JBA) where I purchased and service the car was very good to work with. While the problem was intermittent, it was ultimately reproducible. The full retail price of the ABS Actuator repair was approximately $3,000.
If there is another chapter, I'll update this post.