Komatsu PC100-6 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC100-6 Fault Code S-6?

Fault Code S-6 on the Komatsu PC100-6 indicates a malfunction in the fuel injection system circuit, specifically related to the fuel injection pump solenoid or its control circuit. This code is generated when the Electronic Control Module (ECM) detects abnormal voltage or resistance values from the injection pump solenoid circuit.

This fault directly impacts the fuel delivery system, which regulates engine power output and combustion efficiency. The PC100-6 uses a mechanically-governed fuel injection system with electronic control, making this code critical for maintaining proper engine performance and preventing potential damage from improper fuel delivery ratios.

Common Symptoms

When Code S-6 is active, operators typically experience:

• Engine power loss or hesitation during acceleration, particularly under heavy load conditions
• Erratic engine RPM fluctuations or inability to maintain consistent idle speed
• Hard starting or extended cranking required, especially when the engine is cold
• Black or grey exhaust smoke indicating incomplete combustion from improper fuel metering
• Warning light activation on the instrument cluster, accompanied by diagnostic blink codes

Potential Causes

The most common technical reasons for S-6 activation on used PC100-6 excavators include:

• Fuel injection pump solenoid failure due to internal coil breakdown or mechanical sticking from carbon buildup
• Wiring harness damage at known rub points near the engine mounting brackets or fuel pump assembly
• Corroded or loose electrical connectors at the solenoid terminals, particularly common in machines operating in wet or corrosive environments
• ECM internal fault or poor grounding connections affecting signal integrity
• Damaged wiring insulation from rodent activity or age-related degradation in the engine compartment

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Inspect the fuel injection pump solenoid harness for visible damage, particularly where wiring passes through metal brackets. Check all connector pins for corrosion, bent terminals, or moisture intrusion. On used excavators, this harness frequently shows wear at the fuel pump mounting area.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid resistance across the connector terminals (typical specification: 3-5 ohms). Check for supply voltage (12V) at the connector with ignition on. Verify ground circuit continuity to the ECM, ensuring less than 1 ohm resistance.

Step 3: Solenoid Function Test Disconnect the solenoid and apply direct 12V power to test mechanical operation. Listen for an audible click indicating proper actuation. If the solenoid fails to click or shows resistance outside specifications, replacement is required.

Step 4: ECM Signal Verification Using Komatsu diagnostic software (KOMTRAX compatible tools) or a breakout harness, monitor the PWM signal from the ECM during cranking. Abnormal duty cycle patterns indicate potential ECM issues.

For used machines, thoroughly clean all connector contacts with electrical contact cleaner and apply dielectric grease before reassembly to prevent future corrosion-related faults.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnostic services for complex electrical issues.