Fault Phenomenon: John Deere 850K dozer during operation, the main hydraulic pump emits a high-pitched whine, all actions slow down.

Troubleshooting Process:
– Checked suction line: suction line leaking air or strainer clogged.
– Checked oil level: hydraulic tank oil level too low.
– Checked oil viscosity: oil too thick or too thin.
– Checked pump body: internal pump valve plate worn.

Root Cause: Low hydraulic tank oil level causes main pump cavitation, producing noise and air bubbles.

Required Parts: Add hydraulic oil and check suction line sealing.