Brakes not always responding
 

Hey all! Having issues with my brakes and need some help IDing the problem. I have an 2009 4 door, 2.2L engine model.
_I was going downhill w my foot gently on the brake; hit a bump and then the pedal goes directly to the floor. With a mechanic friend, I replaced the front pads, master cylinder, and flushed it all out. We even did an ABS system flush. The brakes are now 50/50. Sometimes they respond like normal, and other times they go too far and I have to pump the brake to get it where it should.
_I hired a mobile brake specialist to come by and he said it's the ABS module. The kicker is that I'm not getting any ABS warnings, bells, or whistles. Other friends are suggesting calipers...so here we are.

I intend to flush the system again and clean the ABS sensors but I'm curious what could be going on. I don't want to drop $$$ to have an ABS module to be installed and programmed, unless I have to.

TIA, cheers!

Check the booster and the hose for leaks?
Sounds like "blame the computer" syndrome. Did the guy offer any proof, like a code?

He didn't. I'm pretty ignorant to this much brake depth, so I couldn't brain at the time to grill him some questions. After I researched online the whole thing it hit me that there are no error codes or lights to signal an issue...so I'm slowly starting to back away from the ABS module as an error.

No leaks from what I could tell either.

To test booster:
Engine off pump the pedal until hard keep foot on pedal; start engine. pedal should go to floor.

Has anybody inspected? Or adjusted the rear brakes? If you stop and engage the parking brake does it only come up 3 clicks? Or more like 6 to 9 clicks. At 14 years old I would inspect the flex hoses front and rear and the rear wheel cylinders along with adjusting or replacing the shoes and possibly drums.

It doesnt go down to the floor, i have to work it a little bit. However there's a lot of hissing with my brake pedal...air leak?

Bad booster

bad booster or vac leak. I would look closely at the hose for cracks or loose fittings. Your description makes me think something is loose.
But, get the rear brakes adjusted.

Replaced the front pads... did he even look at the rear brakes? I think may be your problem is they're worn out, the adjusters are stuck, and horribly out of adjustment. Overhaul the rear brakes.

You have air in the system.