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

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

Fault Code S-2 on the Komatsu PC50MR-2 indicates a malfunction in the swing motor pressure sensor circuit or an abnormal pressure reading within the swing hydraulic system. This code is part of Komatsu's proprietary diagnostic system that monitors critical hydraulic functions to prevent catastrophic component failure.

The swing motor pressure sensor continuously feeds data to the machine's electronic control module (ECM), allowing the system to regulate hydraulic pressure and protect the swing motor from over-pressurization or starvation. On compact excavators like the PC50MR-2, this monitoring is essential because the swing circuit operates under extreme loads in confined spaces, making early fault detection critical for preventing expensive hydraulic motor damage and maintaining operational safety.

Common Symptoms

When Code S-2 is active, operators typically experience:

• Erratic or sluggish swing operation with inconsistent rotation speeds or complete loss of swing function
• Intermittent warning indicator on the monitor panel, often appearing during heavy swing loads or directional changes
• Reduced hydraulic pressure across multiple functions as the ECM enters protective derate mode
• Abnormal hydraulic noise from the swing motor area, including whining or cavitation sounds
• Error code display on the digital monitor that may reset temporarily but returns under load

Potential Causes

The most common technical reasons for S-2 codes on used PC50MR-2 machines include:

• Damaged or contaminated swing pressure sensor due to hydraulic fluid degradation or moisture ingress (extremely common on machines with 3,000+ hours)
• Corroded or loose electrical connector at the sensor harness—the connector location near the swing motor makes it vulnerable to debris and moisture
• Wiring harness chafing where the sensor cable contacts the swing motor housing or structural frame during rotation cycles
• Failed pressure sensor internal components from age-related dielectric breakdown or mechanical shock
• Contaminated hydraulic oil causing sensor port blockage or false pressure readings
• ECM calibration drift or internal ECM fault (less common but possible on older machines)

How to Troubleshoot and Fix Code S-2

Step 1: Visual Inspection and Connector Check Begin by locating the swing motor pressure sensor on the swing motor assembly. Disconnect the electrical connector and inspect both the sensor pins and harness terminals for corrosion, bent contacts, or moisture contamination. On used excavators, this connector frequently develops green corrosion from water exposure. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Electrical Circuit Testing Using a digital multimeter (DMM), check the sensor circuit. With the ignition on but engine off, measure the reference voltage at the sensor connector (typically 5V ±0.25V). Check ground continuity between the sensor ground pin and chassis ground (should read less than 1 ohm). Inspect the wiring harness along its entire routing path for abrasion points, particularly where it passes near rotating components—a common failure point on the PC50MR-2.

Step 3: Sensor Output Verification With the sensor reconnected and engine running, use Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor live pressure sensor data. Compare readings against specifications (consult service manual for pressure ranges). If readings are erratic, out of range, or show no change during swing operation, replace the pressure sensor. Before installing new components on used machines, verify hydraulic oil quality and check for metal contamination that could damage the replacement sensor.

Step 4: Hydraulic System Verification After sensor replacement, check hydraulic filter condition and oil contamination levels. Perform a swing system pressure test using a calibrated pressure gauge installed at the test port. Verify pressures meet Komatsu specifications during swing operation under load.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex hydraulic-electrical issues, especially on machines still under warranty or service contracts.