What is Komatsu PC110-7 Fault Code S-15?

Fault Code S-15 on the Komatsu PC110-7 excavator indicates a malfunction in the hydraulic pilot system pressure sensor circuit. This code specifically relates to the proportional pressure sensor that monitors pilot oil pressure, which controls the excavator's hydraulic functions including boom, arm, bucket, and swing operations.

The pilot pressure sensor is critical for the PC110-7's electronic control system (ECM) to regulate hydraulic flow and machine responsiveness. When this sensor circuit fails or provides erroneous signals, the ECM cannot properly adjust hydraulic power delivery, leading to compromised machine performance and potential safety concerns. In used excavators, this system is particularly vulnerable due to exposure to hydraulic fluid contamination, vibration damage, and connector corrosion over years of operation.

Common Symptoms

• Sluggish or unresponsive hydraulic controls, especially during initial joystick movement or when multiple functions are operated simultaneously
• Warning light illumination on the instrument panel, often accompanied by an audible alarm from the cab
• Intermittent loss of hydraulic power to specific functions like swing or boom operations
• Erratic machine response where control inputs don't match hydraulic output consistently
• Machine may enter derate mode, limiting engine RPM or hydraulic flow as a protective measure

Potential Causes

On used Komatsu PC110-7 excavators, Code S-15 typically results from several age-related failures:

• Pilot pressure sensor failure due to internal component degradation or hydraulic fluid contamination blocking sensor ports
• Damaged or corroded wiring harness connections, especially at the sensor connector near the main control valve where vibration and hydraulic oil exposure are common
• Broken or chafed wiring along harness routing points under the operator platform or near rotating components
• Poor ground connections at ECM or sensor mounting points due to rust accumulation
• Contaminated hydraulic pilot oil causing sensor reading errors or physical blockage
• ECM internal fault (less common) affecting sensor signal processing circuits

How to Troubleshoot and Fix Code S-15

Step 1: Visual Inspection and Connector Check Begin by locating the pilot pressure sensor mounted on the main control valve assembly beneath the operator cab. Disconnect the sensor electrical connector and thoroughly inspect both the sensor pins and harness terminals for corrosion, bent pins, or hydraulic oil contamination. On used excavators, connector seal failure often allows moisture intrusion. Clean connections with electrical contact cleaner and apply dielectric grease.

Step 2: Sensor Circuit Testing Using a digital multimeter, perform resistance checks on the sensor wiring. With the connector disconnected at the sensor, measure resistance between the signal wire and ground wire at the harness side—you should read open circuit (infinite resistance). Check for short circuits to machine ground on each wire individually. Consult the PC110-7 service manual for specific pin-out diagrams, but typically the sensor uses a 5-volt reference supply, ground, and signal return wire.

Step 3: Sensor Power and Signal Verification Reconnect the harness and back-probe the connector (without disconnecting) using multimeter probes. With the ignition key ON (engine not running), verify 5-volt reference voltage at the appropriate pin. Start the engine and monitor the signal voltage while operating pilot controls—voltage should fluctuate between approximately 0.5-4.5 volts depending on pilot pressure. No change or voltage stuck at extremes indicates sensor failure.

Step 4: Physical Sensor and Hydraulic System Check Remove the pilot pressure sensor from the control valve. Inspect the sensor port for metal debris, sludge buildup, or hydraulic varnish—common in used machines with extended service intervals. Check pilot system hydraulic filter condition and oil quality. Replace contaminated pilot oil and filters before installing a new sensor to prevent repeat failures.

Step 5: Wiring Harness Inspection for Used Equipment Trace the sensor harness from the control valve to the ECM, checking for wire chafing against the frame, heat damage near hydraulic lines, or abrasion points where the harness passes through cab mounting brackets. In used PC110-7 excavators, harness damage frequently occurs where wiring contacts the rotating cab interface or near hydraulic cylinder mounting points.

Step 6: Component Replacement and Code Clearing If testing confirms sensor failure, install a genuine Komatsu replacement sensor (avoid aftermarket sensors that may have incompatible voltage curves). Torque the sensor to specification (typically 15-20 ft-lbs) and apply thread sealant. Use Komatsu diagnostic software (KOMTRAX) or a compatible scan tool to clear the fault code and verify proper sensor operation through live data monitoring.

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Disclaimer: This guide provides general troubleshooting information for Code S-15 on Komatsu PC110-7 excavators. Always consult the official service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.