Hi,
If I understand correctly, the brakes worked when the new MC was installed, and the problem started when the front brakes were replaced.
I have to ask, was the system opened? To replace pads, it shouldn't have needed to be opened. Next, what it sounds like you are referring to is called an automated bleed procedure. The vehicle doesn't have that ability. Here are the bleed directions right from the manual.
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2004 Mazda 6 V6-3.0L DOHC
Procedures
Vehicle Brakes and Traction Control Hydraulic System Brake Bleeding Service and Repair Procedures
PROCEDURES
AIR BLEEDING
Caution: Maintain the fluid level in the reservoir tank proper while bleeding the air.
Specified fluid SAE J1703, FMVSS 116 DOT3
Note: The brakes should be bled whenever a brake line is disconnected. If a hydraulic line is disconnected at the master cylinder, start at the slave cylinder farthest from the brake master cylinder, and move to the next farthest slave cylinder until all four cylinders have been bled. If the disconnection point is anywhere except the master cylinder, start at the point closest to the disconnection, and move to the next closest slave cylinder until all four cylinders have been bled.
1. Remove the bleeder cap and attach a vinyl tube to the bleeder screw.
2. Place the other end of the vinyl tube in a clear, fluid-filled container.
3. One person should depress the brake pedal a few times, and then hold it in the depressed position.
Pic 1
4. A second person should loosen the bleeder screw, drain out the fluid and close the screw using the SST.
Tightening torque
Front: 6.9 - 9.8 Nm (71 - 99 kgf-cm, 62 - 86 inch lbs.)
Rear: 5.9 - 8.8 Nm (61 - 89 kgf-cm, 53 - 77 inch lbs.)
5. Repeat steps 3 and 4 until no air bubbles are seen.
6. Bleed air from each component by following the procedure above.
7. After air bleeding, check the following:
Brake operation
Fluid leakage
Fluid level
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Let me know if this is what was done. Also, you could pressure bleed this system. That is the only other option I know of. One last question. Check the rubber brake hoses in the front and make sure one of them isn't expanding when you press the brakes. You will need a helper for doing that.
I will watch for your reply.
Joe
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Wednesday, December 9th, 2020 AT 7:27 PM