What is Komatsu PC100-6 Fault Code H-8?

Fault Code H-8 on the Komatsu PC100-6 indicates a hydraulic oil temperature sensor abnormality or overheating condition in the hydraulic system. This diagnostic trouble code triggers when the hydraulic oil temperature exceeds the preset threshold (typically above 95-100°C) or when the temperature sensor circuit experiences malfunction.

The hydraulic oil temperature sensor monitors thermal conditions within the excavator's hydraulic system, sending voltage signals to the engine control module (ECM). The PC100-6's hydraulic system is particularly sensitive to temperature fluctuations because excessive heat degrades oil viscosity, reducing lubrication effectiveness and accelerating component wear. On used excavators, this code often appears due to sensor degradation or actual thermal problems caused by years of accumulated debris in cooling circuits.

Common Symptoms

• Audible alarm combined with flashing hydraulic temperature warning light on the instrument panel
• Noticeable reduction in hydraulic response speed and slower cycle times during operation
• Automatic power derate mode where engine RPM limits prevent normal working speeds
• Hydraulic oil appears darker or has a burnt odor during visual inspection
• Intermittent code activation during heavy workloads or hot ambient conditions

Potential Causes

The most frequent causes for H-8 codes on used PC100-6 excavators include:

• Faulty hydraulic oil temperature sensor (resistance drift common after 5,000+ operating hours)
• Blocked hydraulic oil cooler fins filled with debris, mud, or vegetation reducing heat dissipation
• Damaged wiring harness between sensor and ECM, particularly at frame flex points near the swing bearing
• Low hydraulic oil level causing insufficient heat absorption capacity
• Corroded or loose electrical connectors at the temperature sensor mounting location
• Actual hydraulic system overheating from worn pump components or restricted return filters

How to Troubleshoot and Fix Code H-8

Step 1: Visual and Physical Inspection Begin by checking the hydraulic oil cooler for blockages—remove accumulated debris using compressed air. Inspect the oil level at the sight glass; used excavators often develop slow leaks that reduce fluid volume. Examine the sensor wiring harness routing from the hydraulic tank to the ECM, looking for abrasion points, pinched wires, or corroded connectors.

Step 2: Sensor Circuit Testing Using a digital multimeter, measure the temperature sensor resistance at the sensor connector (disconnected). At 20°C ambient temperature, resistance should read approximately 2.0-2.5 kΩ (consult PC100-6 service manual for exact specification). Test for voltage supply from the ECM—should show approximately 5V reference voltage. Check for continuity in the signal wire and ensure ground circuit integrity.

Step 3: Operational Testing and Verification If sensor readings are within specification but the code persists, monitor actual hydraulic oil temperature using an infrared thermometer during operation. Compare readings against sensor output voltage using Komatsu diagnostic software (KOMTRAX or compatible scan tool). For used excavators, replace the hydraulic return filter and verify cooling fan operation before condemning the sensor, as these frequently cause genuine overheating conditions.

Crucial for used equipment: Before replacing the temperature sensor, thoroughly clean all electrical connectors with electrical contact cleaner and apply dielectric grease—corrosion resistance is often the actual fix needed.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC100-6 service manual and consider professional technician assistance for complex hydraulic system repairs.