1. Disconnect the brake fluid level sensor connector from the master cylinder.
2. Inspect for continuity according to fluid level between the brake fluid level sensor terminals.

If not as indicated in the table, replace the reserve tank.

Brake Switch InspectionError Indications (Type A)
If you see an error indication on the
display, find the cause in the chart. If you
cannot clear the error indication, take the
vehicle to an Authorized Mazda Dealer.
Indication
Cause
Solution
CHECK
USB
USB device
malfunction
Verify that the content
...
Brake Hose (Front) Removal/Installation [Mzr 2.0, Skyactiv G 2.0, Mzr 2.5]
1. Remove in the order indicated in the table.
2. Install in the reverse order of removal.
3. Add brake fluid, bleed the brakes, and inspect for leakage after the installation
has been completed..
1
Brake pipe
2
Clip
3
...
Crankshaft Position (CKP) Sensor Inspection [Mzr 2.0, Mzr 2.5]
Visual Inspection
CAUTION:
When foreign material such as an iron chip is on the CKP sensor, it can cause
abnormal output from the sensor because of flux turbulence and adversely affect
the engine control. Be sure there is no foreign material on the CKP sensor when
replacing.
...