Komatsu PC800SE-7 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code S-6?

Fault Code S-6 on the Komatsu PC800SE-7 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 PC800SE-7's operational safety and precision. This hydraulic excavator relies on precise swing control for stability during heavy lifting and positioning 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:

• Erratic swing operation or complete loss of swing brake engagement/disengagement
• Warning indicator illuminated on the monitor panel with S-6 displayed
• Abnormal swing deceleration or failure to hold position on slopes
• Hydraulic pressure fluctuations during swing operations
• Intermittent swing motor performance that worsens as the machine warms up

Potential Causes

The most common technical causes for S-6 on used PC800SE-7 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+ hours)
• Faulty swing pressure sensor providing incorrect feedback to the ECM
• Low hydraulic oil level or contaminated fluid affecting pressure readings
• ECM internal fault or software calibration issues (less common)

How to Troubleshoot and Fix Code S-6

Step 1: Initial Inspection Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to retrieve active and stored codes. Check hydraulic oil level and condition first—contaminated fluid is a frequent culprit in used machines. Inspect the swing motor area for visible oil leaks or damaged harnesses.

Step 2: Electrical Testing Using a digital multimeter, test the swing brake solenoid valve resistance (typically 20-30 ohms when cold). Check for supply voltage (usually 12-24V DC) at the solenoid connector with ignition on. Inspect all connectors and pins for corrosion, bent terminals, or moisture intrusion—critical on used excavators operating in harsh environments.

Step 3: Pressure Sensor Verification Test the swing pressure sensor output voltage (reference Komatsu service manual for specifications, typically 0.5-4.5V range). Check sensor wiring for shorts to ground or opens. On used machines, examine harness routing for wear points where cables contact the swing bearing or frame.

Step 4: Component Replacement If diagnostics confirm component failure, replace the solenoid valve or pressure sensor with genuine Komatsu parts. After replacement, clear codes, perform swing function tests, and monitor for code recurrence over several operating cycles.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC800SE-7 service manual and consider professional technician assistance for complex hydraulic and electrical repairs. Improper diagnosis may lead to equipment damage or safety hazards.