Komatsu 830E-AC Shop Manual page 590

TROUBLE: A Low Brake Pressure Warning Occurs When Brakes are Applied
Leak or other malfunction in one brake circuit.
Brake valve balance is out of adjustment.
TROUBLE: The Low Pressure Warning Circuit Not Operating Properly
The Low Brake Pressure lamp is burned out.
The circuit is open.
Pressure switch defective.
TROUBLE: Low Pressure Warning is On Even Though System Pressure is Proper
Short in electrical system.
Pressure switch is defective.
TROUBLE: Low Pressure Warning Comes On and Pressure is Low
Steering circuit is malfunctioning.
The pump is worn.
TROUBLE: A "Squeal" is Heard When Controller is Operated
Rapid operation of controller.
Brake Valve assembly is damaged.
Hydraulic oil is too hot.
TROUBLE: The Output Pressure At Controller is Correct but Brakes are Not Applying
Brake lines are blocked or improperly connected.
TROUBLE: The Brake Pressures Drift Excessively While Pedal is Held Steady
Contamination in brake valve assembly.
Damage in brake valve assembly.
J4-10 Brake Circuit Check-Out Procedure
Inspect brake system and repair leaks.
Adjust collars according to instructions.
Replace the bulb.
Check the wiring.
Replace the pressure switch.
Check wiring.
Replace the switch.
Check steering circuit pressures.
Rebuild or replace pump.
Normal.
Replace the brake valve assembly.
Check entire hydraulic system for restriction etc.
Check plumbing.
Remove, disassemble, clean, reassemble; or
replace.
Repair or replace brake valve assembly.
J04036