Komatsu PC50MR-2 Fault Code S-15: Complete Diagnostic Guide

What is Komatsu PC50MR-2 Fault Code S-15?

Fault Code S-15 on the Komatsu PC50MR-2 indicates a malfunction in the hydraulic oil temperature sensor circuit. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage reading from the temperature sensor monitoring hydraulic fluid temperature in the main hydraulic system.

The hydraulic oil temperature sensor is critical for the PC50MR-2's performance management system. It protects the hydraulic pump, motors, and cylinders from operating outside safe temperature ranges. When this sensor fails or provides erratic readings, the ECM cannot properly regulate hydraulic system performance, potentially leading to component damage or reduced operational efficiency in this compact excavator.

Common Symptoms

When Code S-15 is active, operators typically experience:

• Warning light illuminated on the instrument panel (typically a hydraulic system indicator)
• Erratic hydraulic performance, including inconsistent swing or bucket speeds
• False temperature warnings appearing even when the machine is cold
• Reduced hydraulic power as the ECM enters a protective derate mode
• Intermittent code activation that may clear and reappear during operation

Potential Causes

The S-15 code in used PC50MR-2 excavators commonly results from:

• Damaged or corroded sensor connector due to exposure to moisture and debris in the hydraulic tank area
• Failed hydraulic oil temperature sensor (common after 4,000-6,000 operating hours)
• Wiring harness damage from rubbing against the hydraulic tank or frame mounting points
• Broken or frayed wires in the sensor circuit between the sensor and ECM
• ECM connector corrosion at pin terminals handling sensor signals
• Poor ground connection affecting sensor voltage reference

How to Troubleshoot and Fix Code S-15

Step 1: Visual Inspection Locate the hydraulic oil temperature sensor on the hydraulic tank (typically mounted near the return filter). Inspect the wiring harness for visible damage, abrasion, or oil contamination. Check the connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators.

Step 2: Electrical Testing Using a digital multimeter, check sensor resistance. Disconnect the sensor connector and measure resistance across sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2.3-2.7 kΩ. Compare readings against Komatsu specifications for your operating temperature.

Step 3: Circuit Voltage Check With the ignition on and sensor disconnected, measure supply voltage at the harness connector. You should see approximately 5 volts from the ECM. If voltage is absent or incorrect, trace the harness back to the ECM, checking for breaks or shorts to ground.

Step 4: Connector and Ground Verification Clean all connector terminals with electrical contact cleaner. For used machines, verify the ground connection at the hydraulic tank mounting point, as corrosion frequently develops here. Check continuity from sensor ground to chassis ground.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu hydraulic temperature sensor (Part #: check your specific serial number). After replacement, clear the fault code using Komatsu diagnostic software or by disconnecting the battery for 30 seconds.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Komatsu PC50MR-2 service manual for your specific machine serial number and seek professional assistance for complex electrical diagnostics or if unfamiliar with excavator systems.