Komatsu PC850SE-8R Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code S-6?

Fault Code S-6 on the Komatsu PC850SE-8R indicates a malfunction in the swing motor system, specifically related to the swing motor brake solenoid valve circuit or pressure sensor abnormality. This code is triggered when the Electronic Control Module (ECM) detects irregular voltage signals, open circuits, or pressure inconsistencies within the swing brake control system.

The swing motor brake system is critical for the PC850SE-8R's operational safety and precision. This hydraulic excavator relies on precise swing control for stability during heavy lifting operations. When S-6 activates, the machine's swing function may become compromised, directly impacting productivity and potentially creating hazardous working conditions on job sites.

Common Symptoms

When fault code S-6 is active, operators typically experience:

• Warning light illumination on the monitor panel with audible alarm
• Reduced swing speed or complete loss of swing function
• Erratic swing brake engagement, causing jerky or unpredictable rotation
• Swing motor fails to hold position on slopes or during load handling
• Derated machine performance with the ECM limiting other hydraulic functions as a safety precaution

Potential Causes

The most common technical causes for S-6 on used PC850SE-8R excavators include:

• Swing brake solenoid valve failure due to internal coil degradation or contaminated hydraulic fluid
• Damaged wiring harness at known rub points near the swing motor mounting area
• Corroded or loose electrical connectors on the solenoid valve circuit (common in machines with 5,000+ operating hours)
• Faulty swing pressure sensor providing incorrect feedback to the ECM
• Low hydraulic pressure in the swing circuit caused by worn pump components
• ECM software glitches or corrupted calibration data in older control modules

How to Troubleshoot and Fix Code S-6

Step 1: Initial Inspection Connect Komatsu diagnostic software (KOMTRAX Plus) or a compatible scan tool to retrieve freeze frame data. Document operating conditions when the fault occurred. Visually inspect the swing motor brake solenoid valve and associated wiring harness for obvious damage, oil contamination, or connector corrosion.

Step 2: Electrical Testing Using a digital multimeter, check the solenoid valve coil resistance (typically 20-30 ohms for Komatsu solenoids). Test for supply voltage at the connector (should read 12-24V depending on system specifications). Inspect ground circuits for continuity and resistance below 5 ohms.

Step 3: Hydraulic System Verification Check swing circuit pressure using a hydraulic pressure gauge at the test port. Compare readings against factory specifications (typically 280-320 bar). Inspect hydraulic fluid quality for contamination or degradation.

Step 4: Component Replacement For used excavators, prioritize replacing the solenoid valve if electrical tests pass but mechanical operation is suspect. Clean all electrical connectors with contact cleaner and apply dielectric grease. Replace any abraded harness sections with proper routing to prevent future wear.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional technician assistance for complex hydraulic system repairs.