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 DiscGear Position Switch Inspection
NOTE
Be sure the transmission and external shift mechanism
are good condition.
Remove the fuel tank (see Fuel Tank Removal in the Fuel
System (DFI) chapter).
Disconnect the connector [A].
Set the hand tester [A] to the × 1 kΩ or × 100 Ω range
and connect i ...
Subthrottle 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
...
ESD (Electronic Steering Damper) ECU Communication Error (Service Code 3C,
ZX1000JD/KD)
ESD ECU Communication Line Inspection
When the data (for status of ESD system) is not sent from
the ESD ECU to the meter unit and ECU, the service code
3C is displayed.
The data is sent through the CAN communication line.
The service code 3C is detected with the meter unit.
The FI symbol does ...