My brakes are suddenly starting to sink to the floor when I'm at a light or just braking. I've noticed it only occurs when the car is on, when the car is off the pressure holds fine and its nice and firm. However as soon as i start up I can hear air and the pedal suddenly sinks after sometime and the idle starts to adjust up and down. Already tried bleeding the car twice, held up fine for like an hour or so but it went soft again. The abs light is also on but won't throw a code when i connect it so thats weird also.. totally lost and would appreciate any help.

 

Empty abs unit,
MC leaking,
abs leaking,
leak some where else in the line.

Check those things.

 

abs unit fluid looks fine, MC is pretty full too, not noticing any leaks around the MC or near the brake pedal are there any test to locate leaks around the system?

possible MC failure? but I'm wondering if i would still suffer because the abs light is on and dont want to change the MC out to find out it was an abs issue.

 

there is definitely a leak somewhere, its brought air into the lines, check the lines that run in to the fender wells, to the caliper have someone press and listen to it sucking in air or possibly spraying out fluid

you will have to find that or else you will be bleeding your brakes very often until the leak expands and they don't hold pressure anywhere

check for warpage on mc cap or abs unit cap, mine was warped and brought in air and leaked

 

damn sounds like a bigger problem then i was hoping for

what exactly would i be looking for on the caps of the MC and abs unit to determine warpage or not

 

If there is no visible leaks then you might have a bad master cylinder seal recirculating inside of itself. Its happened twice on my buddy's civics. He had good pedal sometimes and when he stopped to an idle he lost pedal. Just a thought take it or leave it.

 

Yeah from searching and reading it sounds like my mc is going bad, just wondering now since teh abs light is on would that have any other affect, for some reason when i try to grab the code its not pulling anything just staying solid

 

it doesn't look like i have a leak since my fluid doesn't seem to be draining at any point, would that mean i have a crack somewehre in the lines thats bringing in air?