Komatsu PC220-8 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC220-8 Fault Code H-6?

Fault Code H-6 on the Komatsu PC220-8 indicates a hydraulic system overheat condition, specifically detecting that the hydraulic oil temperature has exceeded the safe operating threshold (typically above 95°C/203°F). This code is triggered when the temperature sensor in the hydraulic tank detects excessive heat, signaling the machine's Electronic Control Module (ECM) that thermal limits have been breached.

This fault is critical for the PC220-8 because sustained high hydraulic temperatures degrade oil viscosity, reduce seal life, and can cause catastrophic hydraulic component failure. The Komatsu PC220-8's closed-center hydraulic system relies on precise oil temperature control to maintain optimal pressure and flow rates.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the monitor panel (red or amber indicator)
• Reduced hydraulic power and sluggish attachment response, especially during sustained operation
• Automatic machine derate limiting engine RPM to protect hydraulic components
• Audible alarm sounding intermittently or continuously when temperatures rise
• Visible heat waves or discoloration around the hydraulic tank on older machines

Potential Causes

Cooling System Issues:

• Blocked or debris-filled hydraulic oil cooler (common on used machines operating in dusty environments)
• Failed cooling fan motor or damaged fan blades reducing airflow
• Malfunctioning fan drive belt causing inadequate cooler performance

Hydraulic Circuit Problems:

• Internal relief valve stuck partially open, creating excessive pressure and heat
• Worn hydraulic pump generating friction heat due to internal leakage
• Restricted return line filters causing back pressure and temperature buildup

Sensor and Electrical:

• Faulty hydraulic temperature sensor providing false readings to the ECM
• Corroded sensor wiring connectors common on machines with 5,000+ hours
• Damaged sensor harness from rubbing against the tank mounting bracket

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Check the hydraulic oil cooler for debris accumulation between fins. On used excavators, this is the most common culprit. Inspect the cooling fan for proper rotation and examine all hoses near the tank for leaks indicating pressure issues.

Step 2: Test Temperature Sensor Using a digital multimeter, measure resistance across the temperature sensor connector (typically located on the left side of the hydraulic tank). Compare readings against Komatsu specifications (usually 200-300 ohms at 20°C). Check for corroded pins or green oxidation at connectors—prevalent on machines stored outdoors.

Step 3: Verify Hydraulic Oil Condition Sample the hydraulic oil and check for darkening or burnt smell indicating thermal breakdown. On used PC220-8s, oil neglect accelerates overheating. Verify oil level meets the sight glass indicator when cold.

Step 4: Pressure Test Relief Valves Connect a pressure gauge to the test port and verify main relief pressure (typically 34.3 MPa/4,970 PSI for the PC220-8). Low pressure suggests internal pump wear; high pressure indicates valve issues.

Step 5: Advanced Diagnostics Use Komatsu KOMTRAX diagnostic software or compatible scan tool to monitor real-time temperature data and verify ECM programming hasn't been corrupted—occasionally seen on machines with aftermarket modifications.

Disclaimer: This guide provides general troubleshooting steps. Always consult certified Komatsu technicians for complex hydraulic system repairs, and refer to the official PC220-8 service manual for torque specifications and detailed procedures.