What is Komatsu PC60-7 Fault Code H-31?

Fault Code H-31 on the Komatsu PC60-7 excavator indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature detected by the machine's monitoring system. This code is triggered when the Electronic Control Module (ECM) receives either an out-of-range signal from the hydraulic oil temperature sensor or detects that oil temperatures have exceeded safe operating thresholds (typically above 100-110°C or 212-230°F).

This fault is critical for the PC60-7 because excessive hydraulic oil temperature can cause rapid degradation of seals, hoses, and hydraulic fluid itself, leading to reduced performance, component damage, and potential system failure. The monitoring system protects expensive hydraulic pumps, motors, and cylinders from heat-related damage.

Common Symptoms

• Hydraulic oil temperature warning light illuminated on the instrument panel (often amber or red)
• Reduced hydraulic performance including slower cycle times and decreased digging force
• Audible warning alarm that sounds intermittently or continuously when oil temperature rises
• Machine entering derate mode or automatic shutdown in severe cases to prevent component damage
• Hot hydraulic oil smell or visible smoke from the hydraulic tank area during operation

Potential Causes

The most common causes of Code H-31 on used Komatsu PC60-7 excavators include:

• Faulty hydraulic oil temperature sensor due to age-related degradation or internal element failure
• Damaged or corroded wiring harness between the sensor and ECM, especially at connection points near the hydraulic tank where heat and vibration cause wear
• Low hydraulic oil level causing inadequate cooling capacity and genuine temperature spikes
• Clogged hydraulic oil cooler fins or radiator blocking proper heat dissipation
• Malfunctioning cooling fan or fan drive circuit preventing adequate airflow
• Degraded hydraulic oil that has lost its thermal properties due to extended service intervals
• Poor electrical ground connections at the sensor mounting point causing erratic signal readings

How to Troubleshoot and Fix Code H-31

Step 1: Visual Inspection and Oil Level Check Begin by checking the hydraulic oil level with the machine on level ground and cylinders retracted. Inspect the hydraulic oil cooler for debris, dirt buildup, or damaged fins. Check that the cooling fan operates properly when the engine reaches operating temperature. On used excavators, examine all visible wiring near the hydraulic tank for signs of chafing, cracking, or oil contamination.

Step 2: Temperature Sensor Testing Locate the hydraulic oil temperature sensor (typically mounted on or near the hydraulic tank). Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture—common issues in older machines. Using a digital multimeter, measure the sensor's resistance at ambient temperature. For the PC60-7, resistance should typically read between 200-400 ohms at 20°C (68°F), decreasing as temperature rises. Compare readings against Komatsu specifications. Also check for proper continuity to ground through the sensor body.

Step 3: Wiring Harness and ECM Circuit Verification With the sensor disconnected, measure voltage supply at the harness connector (should typically be 5V reference voltage from the ECM). Check signal wire continuity from the sensor connector back to the ECM using a wiring diagram. Pay special attention to harness routing points where friction against the frame or hydraulic lines may have worn through insulation—a frequent problem on used equipment with 5,000+ operating hours.

Step 4: Verify Actual Oil Temperature Use an infrared thermometer or contact thermometer to measure actual hydraulic oil temperature at the tank. If the measured temperature is normal (below 80°C/176°F) but the code persists, the sensor or circuit is likely faulty. If temperature is genuinely high, address cooling system issues before replacing electrical components.

Step 5: Component Replacement and Testing Replace the temperature sensor with a genuine Komatsu part or quality aftermarket equivalent if testing confirms failure. Always apply dielectric grease to connectors during reassembly to prevent future corrosion. After replacement, clear the fault code using Komatsu diagnostic software or by disconnecting the battery for 10 minutes. Operate the machine through a complete work cycle and monitor for code recurrence.

Disclaimer: This guide provides general troubleshooting information for experienced technicians and equipment owners. Always consult the official Komatsu PC60-7 service manual and safety procedures. If uncertain about any diagnostic or repair procedure, contact a certified Komatsu technician or authorized service center to prevent equipment damage or personal injury.