Inspect the PCM. (See PCM INSPECTION.)
Mazda 6 Service Manual: Solenoid valve removal/installation
1. Disconnect the negative battery cable.
2. Remove the under cover.
3. Remove the control valve body. (See CONTROL VALVE BODY REMOVAL.)
4. Remove the solenoid valve(s).
5. Apply ATF to a new O-ring and install it on the solenoid valve.
6. Install the solenoid valve in the control valve body. ...
Mazda 6 Service Manual: Antilock Brake System (ABS)
The ABS control unit continuously monitors the speed of each wheel. If one wheel
is about to lock up, the ABS responds by automatically releasing and reapplying
that wheel's brake.
The driver will feel a slight vibration in the brake pedal and may hear a chattering
noise from the brake system ...