Internal leakage​ – Excessive wear causing low flow/pressure.

Shaft seal failure​ – External hydraulic oil leakage.

Bearing wear/noise​ – Causing vibration and potential shaft damage.

Cavitation damage​ – From air ingress or restricted inlet flow.

Overheating​ – Due to inefficiency, high load, or poor cooling.

Pressure loss/drop​ – Inability to reach or maintain rated pressure.

Low flow output​ – Reduced machine speed and weak performance.

Erratic operation​ – Surging or inconsistent hydraulic action.

Unusual noise (whine/knock)​ – Indicating wear or cavitation.

Case drain flow excessive​ – Sign of severe internal wear.

Control response sluggish​ – Slow reaction to operator commands.

Pump housing cracks​ – From stress, freezing, or impact.

Coupling/shear pin failure​ – Due to shock load or misalignment.

Contamination damage​ – From abrasive particles in the oil.

Swashplate/cylinder wear​ – In variable displacement pumps.

Valve plate scoring​ – Leading to internal leakage and heat.

Slipper pad wear​ – Causing noise and loss of efficiency.

Servo piston sticking​ – In variable pumps, causing control failure.

Charge pump failure​ – In closed-loop systems, causing weak steering/travel.

Pressure compensator fault​ – Failing to maintain set pressure.

Flow compensator fault​ – Failing to deliver demanded flow.

Solenoid valve failure​ – In electronically controlled pumps.

Sensor failure (pressure/displacement)​ – Sending erroneous signals to controller.

Mounting bolt loosening​ – Causing misalignment and vibration.

Oil aeration​ – Pump drawing in air, causing noise and damage.

Water contamination​ – Leading to corrosion and reduced lubrication.

Incorrect oil viscosity​ – Causing poor lubrication or high resistance.

Over-pressurization​ – From relief valve failure, damaging internals.

Fatigue failure​ – Of internal components from cyclic loading.

General efficiency degradation​ – Gradual loss of performance and increased fuel consumption.