Komatsu PC450-6 Fault Code H-27: Complete Diagnostic Guide

What is Komatsu PC450-6 Fault Code H-27?

Fault Code H-27 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC450-6 excavator. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, which monitors the operating temperature of the hydraulic system fluid.

The hydraulic oil temperature sensor plays a critical role in protecting the PC450-6's hydraulic system from overheating damage. When functioning properly, it allows the ECM to adjust pump output and activate warning systems before temperatures reach dangerous levels. For used excavators, this sensor circuit is particularly vulnerable to degradation from years of exposure to heat, vibration, and contamination.

Common Symptoms

When Code H-27 is active, operators typically experience:

• Hydraulic oil temperature warning light illuminated on the instrument panel
• Erratic temperature gauge readings or gauge stuck at maximum/minimum positions
• Reduced hydraulic system performance as the ECM enters protective derate mode
• Intermittent code activation during warm-up or under heavy load conditions
• Audible warning alarm in some PC450-6 configurations when temperature monitoring fails

Potential Causes

The most common technical causes for H-27 on used PC450-6 excavators include:

• Failed hydraulic oil temperature sensor due to internal element degradation or contamination exposure
• Damaged sensor wiring harness at known rub points near the hydraulic tank mounting bracket
• Corroded or loose electrical connectors at the sensor or ECM interface
• Short circuit or open circuit in the sensor signal wire from harness chafing
• ECM internal fault (rare, but possible in high-hour machines)
• Poor ground connections at the sensor mounting location due to rust or paint buildup

How to Troubleshoot and Fix Code H-27

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor (typically mounted on the hydraulic tank). Inspect the sensor connector for corrosion, oil contamination, or loose pins. Check the wiring harness along its entire route for abrasion, especially where it contacts frame members or hydraulic lines—a common failure point on used machines.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures (consult Komatsu specifications, typically 200-400 ohms at 20°C). Test the harness continuity from sensor connector to ECM. Check for voltage supply (typically 5V reference) at the sensor connector with ignition on.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or harness shows damage, replace the faulty component. For used excavators, always apply dielectric grease to connectors and secure harnesses with new zip ties away from wear points. Clear the code using Komatsu diagnostic software and monitor during a full operating cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC450-6 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.