Komatsu PC800-7 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code H-6?

Fault Code H-6 on the Komatsu PC800-7 indicates a hydraulic oil temperature sensor circuit malfunction or abnormally high hydraulic oil temperature. This code is triggered when the Electronic Control Module (ECM) detects either an electrical fault in the temperature sensor circuit or when hydraulic oil temperature exceeds the manufacturer's safe operating threshold (typically above 110-120°C or 230-248°F).

This fault is critical for the PC800-7 because excessive hydraulic oil temperature can cause rapid degradation of seals, accelerated component wear, and reduced hydraulic system efficiency. The hydraulic temperature sensor monitors oil temperature in the main hydraulic tank and sends voltage signals to the controller, which adjusts pump output and activates warning systems to prevent catastrophic system failure.

Common Symptoms

When Code H-6 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the monitor panel (red or amber indicator)
• Reduced hydraulic performance including slower cycle times and decreased lifting capacity
• Automatic engine derate or speed limitation to protect the hydraulic system
• Audible warning alarm sounding continuously or intermittently
• Visible steam or excessive heat radiating from the hydraulic tank area in severe cases

Potential Causes

The most common technical causes for H-6 on used PC800-7 excavators include:

• Faulty hydraulic oil temperature sensor due to internal element failure or contamination exposure
• Damaged wiring harness or corroded connectors between the sensor and ECM (common at frame flex points near the tank)
• Actual hydraulic oil overheating caused by restricted hydraulic oil cooler, low coolant levels, or failed cooling fan
• Clogged hydraulic return filters creating excessive back pressure and heat generation
• Degraded hydraulic oil with reduced thermal properties from extended service intervals
• Short circuit or open circuit in the sensor signal wire (typically 5V reference circuit)

How to Troubleshoot and Fix Code H-6

Step 1: Visual Inspection Check the hydraulic oil temperature sensor location (typically mounted on the hydraulic tank). Inspect the connector for corrosion, oil contamination, or damaged pins. On used excavators, examine the wiring harness for chafing against the frame or hydraulic lines—a common wear point on the PC800-7.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Check for 5V reference voltage at the harness connector with ignition on. Verify ground continuity between the sensor ground pin and chassis ground (should read less than 1 ohm).

Step 3: Physical System Check If electrical tests pass, verify actual hydraulic oil temperature with an infrared thermometer. Check hydraulic oil level, inspect the oil cooler for debris blockage, and verify cooling fan operation. Replace hydraulic filters if service intervals have been exceeded.

Step 4: Component Replacement Replace the temperature sensor if resistance values are out of specification or if the sensor shows physical damage. For used machines, always apply dielectric grease to connectors during reassembly to prevent future corrosion.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional consultation for complex repairs. Improper diagnosis can lead to equipment damage or safety hazards.