What is Komatsu PC220-8 Fault Code H-5?

Fault Code H-5 on the Komatsu PC220-8 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature. This code is generated when the Engine Control Module (ECM) or Monitor Control Unit (MCU) detects either a circuit irregularity in the hydraulic oil temperature sensor or that hydraulic oil temperature has exceeded the safe operating threshold (typically above 110°C/230°F).

The hydraulic system is the lifeblood of any excavator, and maintaining proper oil temperature is critical for viscosity, component longevity, and safe operation. On the PC220-8, excessive heat or faulty sensor readings can trigger protective derating modes that reduce hydraulic pump output, potentially bringing operations to a halt. For used machines, this code often reveals accumulated wear in cooling circuits or degraded sensors that require immediate attention.

Common Symptoms

When fault code H-5 is active on your Komatsu PC220-8, operators typically experience:

• Warning light or alarm displayed on the monitor panel indicating high hydraulic temperature
• Reduced hydraulic performance including slower cycle times and weak digging force as the system enters protective mode
• Audible alarm from the cab that sounds when hydraulic temperature exceeds safe limits
• Hot hydraulic oil odor or visible heat shimmer near the hydraulic tank or cooler
• Error message on LCD display specifically referencing hydraulic oil temperature

Potential Causes

Several technical issues can trigger H-5 on used PC220-8 excavators:

• Faulty hydraulic oil temperature sensor – Common failure point on machines with 5,000+ hours; sensor resistance drifts outside specification range
• Damaged or corroded wiring harness – Particularly at connector points near the hydraulic tank where vibration and heat exposure cause deterioration
• Clogged hydraulic oil cooler – Debris buildup between cooling fins restricts airflow, especially in demolition or dusty environments
• Low hydraulic oil level – Reduces heat dissipation capacity and can expose the temperature sensor
• Malfunctioning cooling fan – Fan motor failure or damaged fan blades reduce cooler effectiveness
• Degraded hydraulic oil – Old or contaminated oil loses heat transfer properties
• ECM/MCU communication errors – Rare but possible on older machines with electrical system corrosion

How to Troubleshoot and Fix Code H-5

Step 1: Verify Actual Hydraulic Oil Temperature

Use an infrared thermometer to measure the actual hydraulic oil temperature at the tank. Compare this reading to what the monitor displays. If the physical temperature is below 100°C but the code persists, suspect a sensor or wiring fault rather than actual overheating.

Step 2: Inspect the Hydraulic Oil Temperature Sensor

Located on the hydraulic tank, disconnect the temperature sensor connector and inspect for corrosion, bent pins, or moisture intrusion—extremely common on used excavators. Use a digital multimeter to measure sensor resistance at ambient temperature (should typically read 200-300 ohms at 20°C; consult the service manual for exact specifications). Replace the sensor if resistance is out of range or shows an open/short circuit.

Step 3: Check Wiring Harness Continuity

Trace the sensor harness from the tank to the MCU/ECM, looking for chafing points, especially where the harness routes near moving components or sharp edges. Check continuity and insulation resistance using a multimeter. On used machines, pay special attention to connector seals and grounds, as vibration over years causes wire fatigue.

Step 4: Examine the Hydraulic Cooling System

Inspect the hydraulic oil cooler for blocked fins, damaged cores, or debris accumulation. Check that the cooling fan operates when hydraulic temperature rises—test fan motor voltage and verify blade condition. Clean the cooler thoroughly with compressed air or pressure washer.

Step 5: Verify Hydraulic Oil Condition and Level

Check hydraulic oil level according to manufacturer specifications and inspect oil quality. Dark, burnt-smelling oil indicates thermal breakdown and requires complete system flushing and fresh ISO VG 46 hydraulic oil. Old oil cannot dissipate heat effectively.

Step 6: Use Komatsu Diagnostic Software

Connect KOMTRAX or Komatsu diagnostic software to read real-time sensor values, freeze frame data, and confirm whether H-5 is temperature-related or purely electrical. This step definitively isolates sensor faults from actual overheating conditions.

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Disclaimer: This guide provides general troubleshooting information for Komatsu PC220-8 fault code H-5. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis from a certified Komatsu technician, especially when dealing with complex electrical or hydraulic systems on used equipment.