If a master cylinder or piston shows any damage, replace them.

If a cup is worn, damaged softened (rotted), or swollen, the piston assembly should be replaced to renew the cups.
If fluid leakage is noted at the brake lever, the piston assembly should be replaced to renew the cups.
If they are damaged, replace them.
If the springs are damaged, replace them.
If the relief port becomes plugged, the brake pads will drag on the disc. Blow the ports clean with compressed air.
Front Master Cylinder [I] Rear Master Cylinder [J]

Rear Master Cylinder Installation
Brake DiscSubthrottle Sensor Output Voltage Inspection
Measure the output voltage at the subthrottle sensor in
the same way as input voltage inspection, note the following.
Disconnect the subthrottle sensor connector and connect
the setting adapter [A] between these connectors.
Special Tool - Throttle Sensor Setting Adapter: 57001
-1538
...
Air Intake Solenoid Valve (Service Code 2d, Equipped Models)
Air Intake Solenoid Valve Removal/Installation
Refer to the Air Intake Solenoid Valve Removal/Installation
in the Fuel System (DFI) chapter.
Air Intake Solenoid Valve Inspection
Refer to the Air Intake Solenoid Valve Unit Test in the
Electrical System chapter.
If the air intake ...
Gear Position Switch Output Voltage Inspection
NOTE
Be sure the battery is fully charged.
Turn the ignition switch to OFF.
Remove the fuel tank (see Fuel Tank Removal in the Fuel
System (DFI) chapter).
Disconnect the sidestand switch/gear position switch lead
connector [A].
Connect the measuring adapter [A] between the ...