Komatsu PC35MR-2 Fault Code H-6: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code H-6?

Fault Code H-6 on the Komatsu PC35MR-2 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature exceeding system parameters. This code specifically relates to the hydraulic temperature monitoring circuit, which safeguards the machine's hydraulic system from overheating damage.

The hydraulic oil temperature sensor sends critical data to the machine's ECM (Engine Control Module), allowing it to monitor operating conditions and prevent catastrophic component failure. On compact excavators like the PC35MR-2, maintaining proper hydraulic temperature is essential for seal integrity, pump longevity, and consistent operational performance. When this code triggers, the machine may enter derate mode to protect internal components.

Common Symptoms

When Code H-6 is active on your PC35MR-2, you may experience:

• Hydraulic temperature warning light illuminated on the instrument panel
• Reduced hydraulic performance or sluggish boom/bucket response, especially during extended operation
• Intermittent machine shutdown or refusal to start when hydraulic oil is excessively hot
• Visible smoke or burning smell from the hydraulic tank area in severe overheating cases
• Error message display on multi-function monitor (if equipped)

Potential Causes

Several factors commonly trigger H-6 on used PC35MR-2 excavators:

• Faulty hydraulic oil temperature sensor due to age-related degradation or internal short circuit
• Damaged wiring harness near the hydraulic tank, particularly at rub points where the harness contacts metal edges
• Corroded or loose electrical connectors at the sensor connection point (common in machines exposed to moisture)
• Actual hydraulic oil overheating caused by clogged hydraulic oil cooler, low oil level, or degraded oil viscosity
• Blocked hydraulic cooling fan or damaged fan motor reducing airflow
• ECM calibration issues or software glitches storing false temperature readings

How to Troubleshoot and Fix Code H-6

Step 1: Initial Visual Inspection Check hydraulic oil level and condition first. Inspect the hydraulic oil cooler for debris blockage, bent fins, or restricted airflow. On used excavators, verify the cooling fan operates correctly during high-temperature conditions.

Step 2: Test the Temperature Sensor Locate the hydraulic oil temperature sensor on the hydraulic tank. Disconnect the electrical connector and inspect for corrosion or moisture intrusion—extremely common failure points on older machines. Using a digital multimeter, measure sensor resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C, consult service manual for exact specifications). Compare readings against Komatsu's resistance-temperature chart.

Step 3: Wiring Harness Verification Trace the sensor wiring harness from the sensor to the ECM connection, checking for abrasion points, damaged insulation, or pinched wires. Pay special attention to areas where harnesses route near moving components or sharp frame edges. Measure circuit voltage at the ECM connector (should read approximately 5V reference voltage with key on, engine off).

Step 4: Functional Testing If sensor and wiring test within specifications, monitor actual hydraulic oil temperature with an infrared thermometer during operation. Compare physical temperature to ECM-reported values using Komatsu diagnostic software (KOMTRAX or compatible scan tool). A discrepancy indicates ECM communication issues or calibration drift.

Step 5: Component Replacement Replace the temperature sensor first if readings are out of specification or erratic. For used excavators, always apply dielectric grease to electrical connections during reassembly to prevent future corrosion. Clear codes and perform operational testing under load.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC35MR-2 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with hydraulic systems. Improper repairs may void warranties or create safety hazards.