Komatsu PC35MR-2 Fault Code H-5: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code H-5?

Fault Code H-5 on the Komatsu PC35MR-2 indicates a hydraulic oil temperature sensor malfunction or abnormally high hydraulic oil temperature. This code triggers when the machine's electronic control unit (ECU) detects that hydraulic fluid temperature exceeds safe operating parameters (typically above 110°C/230°F) or when the temperature sensor circuit sends irregular signals.

This fault is critical for the PC35MR-2 because excessive hydraulic oil temperature degrades fluid viscosity, reduces lubrication efficiency, and accelerates seal deterioration. The excavator's compact design means the hydraulic system operates under high pressure in tight spaces, making temperature management essential for component longevity.

Common Symptoms

When Code H-5 is active, operators typically experience:

• Temperature warning light illuminated on the instrument panel (often red or amber)
• Sluggish hydraulic response during boom, arm, or bucket operations due to reduced fluid efficiency
• Automatic power derate limiting engine RPM to protect hydraulic components
• Unusual whining or cavitation noises from the hydraulic pump during operation
• Intermittent shutdowns if the ECU enters protective mode to prevent system damage

Potential Causes

The most common technical failures triggering H-5 on used PC35MR-2 excavators include:

• Faulty hydraulic oil temperature sensor (common failure point after 3,000+ operating hours)
• Clogged hydraulic oil cooler fins or passages restricting heat dissipation
• Damaged wiring harness near the hydraulic tank, especially where cables contact frame edges (known wear point on this model)
• Degraded hydraulic oil with contaminated or broken-down additives reducing heat transfer
• Malfunctioning cooling fan or faulty fan relay preventing adequate airflow
• Corroded sensor connector pins at the harness junction behind the operator's cab

How to Troubleshoot and Fix Code H-5

Step 1: Visual Inspection Begin by inspecting the hydraulic oil cooler for debris, mud, or damaged fins. On used machines, check the wiring harness routing from the temperature sensor (located on the hydraulic tank side) for chafing, cuts, or oil contamination. Examine the sensor connector for corrosion or bent pins—this is a frequent issue on excavators operated in wet conditions.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the temperature sensor connector and measure resistance across the sensor terminals. At 20°C (68°F), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness for continuity to the ECU and check for short circuits to ground.

Step 3: Hydraulic System Evaluation Check actual hydraulic oil temperature with an infrared thermometer during operation. If oil exceeds 95°C (203°F) but the sensor reads correctly, investigate cooling system failures: verify the cooling fan operates when hydraulic temp rises, inspect for coolant leaks affecting the oil cooler heat exchanger, and analyze hydraulic fluid condition (change if darkened or burnt-smelling).

Step 4: Component Replacement If diagnostics confirm sensor failure, replace the hydraulic oil temperature sensor (Komatsu part reference: verify with dealer). For used excavators, always apply dielectric grease to connector pins during reassembly to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or by disconnecting the battery for 10 minutes.

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Disclaimer: This guide provides general diagnostic information. Hydraulic systems operate under extreme pressure and temperature. Always consult a certified Komatsu technician and refer to the official PC35MR-2 service manual before performing repairs. Improper diagnosis may result in equipment damage or personal injury.