Komatsu PC60-7 Fault Code S-6: Complete Technical Guide

What is Komatsu PC60-7 Fault Code S-6?

Fault Code S-6 on the Komatsu PC60-7 indicates a malfunction in the hydraulic oil temperature sensor circuit or abnormally high hydraulic oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either a sensor signal outside the normal operating range (typically 0.5-4.5V) or when hydraulic oil temperatures exceed approximately 90-95°C (194-203°F).

This fault is critical for the PC60-7 because excessive hydraulic temperatures can cause rapid degradation of seals, reduced hydraulic efficiency, and potential component seizure. The hydraulic oil temperature sensor plays a vital role in protecting the hydraulic pump, control valves, and cylinder seals from thermal damage. In used excavators, this code often appears due to sensor degradation or accumulated deposits affecting heat dissipation.

Common Symptoms

• Hydraulic temperature warning light illuminated on the instrument panel (amber or red depending on severity)
• Sluggish hydraulic response or reduced cycle times as oil viscosity decreases with heat
• Audible alarm or intermittent beeping from the cab warning system
• Automatic engine RPM reduction (derate mode) to protect hydraulic components
• Hot hydraulic oil smell or visible heat waves from the hydraulic tank area during operation

Potential Causes

Sensor-Related Issues:

• Faulty hydraulic oil temperature sensor (resistance drift common in machines with 5,000+ hours)
• Damaged or corroded sensor wiring harness, particularly where it passes near the hydraulic tank mounting brackets
• Poor ground connection at the sensor or ECM grounding point

Actual Temperature Issues:

• Clogged hydraulic oil cooler fins (debris accumulation typical in dusty jobsites)
• Low hydraulic oil level reducing thermal capacity
• Worn hydraulic pump creating excessive internal leakage and heat generation
• Restricted cooling fan operation or damaged fan shroud
• Use of incorrect hydraulic oil viscosity grade (common in used equipment with unknown service history)

How to Troubleshoot and Fix Code S-6

Step 1: Verify Actual Hydraulic Temperature Use an infrared thermometer to measure actual hydraulic tank temperature. Compare this reading to the temperature sensor reading displayed in your Komatsu diagnostic software (KOMTRAX or compatible tool). A variance greater than 10°C indicates sensor or wiring issues rather than actual overheating.

Step 2: Inspect Temperature Sensor and Wiring Locate the hydraulic oil temperature sensor (typically mounted on the hydraulic tank side panel). Disconnect the sensor connector and inspect for:

• Corrosion or oil contamination in pin terminals
• Harness chafing where cables contact metal edges (common wear point on used PC60-7 models)
• Check sensor resistance values with a multimeter: should read approximately 200-300 ohms at 20°C (varies with temperature)

Step 3: Test Sensor Circuit Voltage With ignition ON and sensor disconnected, check supply voltage at the harness connector: should read 5V ± 0.5V. Check signal wire continuity back to the ECM. In used excavators, corrosion in the bulkhead connectors near the cab mount frequently causes intermittent faults.

Step 4: Address Cooling System Issues If sensor tests pass, inspect the hydraulic oil cooler for blockages. Remove debris with compressed air (blow from inside out). Check cooling fan belt tension and fan clutch operation. Verify hydraulic oil level and condition—contaminated oil in used machines often contains metal particles that reduce cooling efficiency.

Step 5: Replace Components as Needed Replace the temperature sensor if resistance values are out of specification (OEM part: 21N-04-13180). For persistent high-temperature issues, consider hydraulic pump efficiency testing as internal wear is common in higher-hour used excavators.

Disclaimer: This guide provides general troubleshooting procedures. Hydraulic system repairs involve high-pressure components and specialized tools. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues or major component replacement.