Komatsu PC35MR-2 Fault Code H-15: Technical Guide

What is Komatsu PC35MR-2 Fault Code H-15?

Fault Code H-15 indicates a hydraulic oil temperature sensor circuit malfunction in the Komatsu PC35MR-2 compact excavator. This code triggers when the Electronic Control Module (ECM) detects abnormal voltage readings from the hydraulic oil temperature sensor, which monitors fluid temperature in the hydraulic system.

The hydraulic oil temperature sensor plays a critical role in protecting the PC35MR-2's hydraulic components from overheating damage. When this sensor fails or sends erratic signals, the ECM cannot accurately monitor system temperatures, potentially leading to reduced machine protection and performance limitations. For used excavators, this fault often stems from sensor degradation or wiring issues common in machines with 3,000+ operating hours.

Common Symptoms

• Warning light illumination on the instrument panel, often accompanied by a hydraulic temperature indicator
• Reduced hydraulic performance or slower cycle times as the ECM enters protective derate mode
• Intermittent code activation, especially during temperature fluctuations or when the machine warms up
• Erratic temperature gauge readings showing unrealistic temperature spikes or drops
• Machine may limit operations to protect hydraulic components from potential thermal damage

Potential Causes

The most common causes of Code H-15 on used PC35MR-2 excavators include:

• Failed hydraulic oil temperature sensor due to age, thermal cycling, or internal component breakdown
• Damaged wiring harness near the hydraulic tank area where cables experience vibration and heat exposure
• Corroded or loose electrical connectors at the sensor plug, particularly in machines exposed to moisture
• Shorted or open circuits in the sensor signal wire between the sensor and ECM
• ECM internal issues (rare) affecting the sensor input circuit
• Poor electrical grounds causing voltage reference problems in the sensor circuit

How to Troubleshoot and Fix Code H-15

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor mounted on the hydraulic tank. Inspect the wiring harness for obvious damage, abrasion points, or areas where cables rub against metal components—common on used excavators. Check the connector for corrosion, moisture intrusion, or bent pins. Clean connectors with electrical contact cleaner and ensure secure connections.

Step 2: Sensor Circuit Testing Using a digital multimeter, check the sensor's resistance at varying temperatures (consult Komatsu specifications, typically 200-300 ohms at 68°F). Disconnect the sensor connector and measure voltage supply from the ECM (should be approximately 5 volts). Test continuity in the signal wire from sensor to ECM and verify the ground circuit integrity.

Step 3: Component Replacement and Verification If sensor resistance values are out of specification or the wiring shows damage, replace the faulty component. For used excavators, always inspect the new sensor's mounting location for debris or metal shavings that could affect readings. After repairs, clear the code using Komatsu diagnostic software or by disconnecting the battery for 5 minutes. Monitor the system during a complete warm-up cycle to confirm proper operation.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance for complex electrical diagnostics or if you're unsure about any procedure.