2009 Frontier brake bleed issue?

[ChadS]

I have a 2009 nissan frontier with traction control. I was having problems with the pedal sinking to the floor so I replace the master cylinder. I performed a bench bleed on the MC and brake bleed on all wheels. The pedal is better and no longer sinking to the floor but it still feels spongy. Does anyone have some tips on how to improve the pedal response?

[VStar650CL]

The FSM won't say it, but the ABS's have their own internal reservoirs which may also need to be bled when replacing a MC. Just bleeding the MC and wheels won't always do it. Either disconnect the battery or pop the ABS connector while bleeding. Do the two ABS inlet lines first and then the four outlets, then re-bleed the wheels.

Also, while the MC was out, did you inspect the booster to make sure there was no intrusion of brake fluid? That can happen when a MC rear seal goes bad, and resulting softening of the rubber diaphragm will usually cause sponge in the pedal.

[ChadS]

I forgot to disconnect the ABS connector during the bleed process. Will this cause air to be stuck in the ABS during a wheel bleed?

[VStar650CL]

No, it's just a safety precaution. Even though the controller is supposed to be dead with the key off, the solenoids still have battery power. So Nissan recommends disconnecting the unit to prevent issues in case there's an undiagnosed board failure.