What is Komatsu PC110-7 Fault Code S-6?

Komatsu PC110-7 Fault Code S-6 indicates a malfunction in the swing motor control system, specifically related to the swing motor solenoid valve or its associated control circuit. This code is triggered when the ECM (Engine Control Module) detects an abnormal electrical signal or performance issue within the swing motor's hydraulic control circuitry.

The swing motor control system is critical for the PC110-7's upper structure rotation, allowing the operator to position the boom and attachment precisely. When fault code S-6 activates, the machine's hydraulic pilot system cannot properly regulate swing speed or direction, directly impacting productivity and operator safety. This code is particularly common in used excavators where electrical connectors and solenoid valves have accumulated thousands of operating hours under harsh conditions.

Common Symptoms

When fault code S-6 is active on your Komatsu PC110-7, you may experience:

• Erratic swing operation – the upper structure may rotate inconsistently or fail to respond smoothly to joystick inputs
• Complete loss of swing function – the machine cannot rotate, leaving the operator unable to reposition the boom
• Warning lamp illumination on the instrument cluster, often accompanied by an audible alarm
• Intermittent swing behavior that worsens as hydraulic oil temperature increases during operation
• Reduced swing speed or inability to achieve full rotational RPM under load

Potential Causes

Fault code S-6 typically stems from these technical issues, especially in used machinery:

• Failed swing motor solenoid valve – internal coil burnout or mechanical sticking due to contaminated hydraulic fluid
• Damaged wiring harness at known rub points near the swing bearing or center joint, where flexing causes wire breakage
• Corroded electrical connectors on the solenoid valve plug, particularly on machines operated in coastal or high-moisture environments
• ECM internal fault affecting the output driver circuit for the swing motor control
• Hydraulic pilot pressure sensor malfunction sending incorrect signals to the control system
• Short circuit to ground in the solenoid valve wiring due to insulation degradation over time

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Begin by thoroughly inspecting the swing motor solenoid valve wiring harness from the ECM connector to the valve itself. On used PC110-7 excavators, check for wire chafing near the swing bearing where the harness passes through the center joint. Look for pinched wires, melted insulation, or oil-soaked connections that indicate previous hydraulic leaks.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure resistance across the solenoid coil terminals. Komatsu specifications typically call for 8-15 ohms at room temperature. Also check for continuity to ground on each wire – any reading below infinite resistance indicates a short circuit requiring harness replacement.

Step 3: Solenoid Valve Function Test With the connector attached and ignition on (engine off), use a Komatsu diagnostic software tool or backprobe the connector to verify the ECM is sending proper 12V command voltage when swing function is activated. No voltage indicates an ECM driver failure; voltage present with no valve action confirms solenoid valve replacement is needed.

Step 4: Connector and Ground Verification Clean all electrical connectors with contact cleaner and apply dielectric grease. On used excavators, corrosion at the X-joint connector is extremely common. Verify the swing motor ground strap has solid continuity to the chassis; loose grounds cause erratic code behavior.

Disclaimer: This guide provides general troubleshooting procedures for Komatsu PC110-7 fault code S-6. Always consult the manufacturer's official service manual and consider professional diagnosis for complex electrical or hydraulic system repairs, especially on used equipment with unknown service history.