What is Komatsu PC210LC-7 Fault Code S-8?

Fault Code S-8 on the Komatsu PC210LC-7 indicates a malfunction in the engine controller (ECM) power supply circuit or an abnormal voltage condition affecting the main power relay system. This code specifically relates to the electrical power distribution that keeps the Engine Control Module (ECM) operational and communicating with sensors and actuators throughout the machine.

This fault is critical because the ECM serves as the central brain of the excavator's engine management system, controlling fuel injection timing, throttle response, and emissions systems. When power supply integrity is compromised, the ECM cannot maintain proper engine performance, potentially causing unexpected shutdowns or preventing startup altogether. On used PC210LC-7 models, this code often surfaces due to aging electrical components and corrosion in the power distribution circuit.

Common Symptoms

• Engine cranks but fails to start, or starts then immediately shuts down after a few seconds
• Intermittent power loss to the monitor panel, with gauges flickering or going dark during operation
• Main relay clicking repeatedly from the electrical panel area behind the operator's seat
• Battery warning light illuminates on the instrument cluster even when charging system tests normal
• Complete loss of ECM communication when attempting diagnostics with Komatsu diagnostic software

Potential Causes

The most common technical causes for Code S-8 on used PC210LC-7 excavators include:

• Failed main power relay (located in the electrical junction box under the operator's cab) - particularly common after 8,000+ operating hours
• Corroded or loose power supply connectors at the ECM harness, especially the main 32-pin connector which is vulnerable to moisture intrusion
• Damaged wiring harness between the battery disconnect switch and ECM, often caused by rubbing against frame rails near the fuel tank mounting area
• Degraded battery cables or poor ground connections at the frame grounding points, creating voltage drop issues
• Internal ECM power circuit failure from voltage spikes or previous jump-start damage on used machines

How to Troubleshoot and Fix Code S-8

Step 1: Verify Power Supply Voltage Using a digital multimeter, check battery voltage at the terminals (should read 12.4-12.8V with engine off). Then measure voltage at the ECM main power supply pin (Pin 1 on the 32-pin connector) with the key switch in the ON position—it should read full battery voltage. If voltage is below 11.5V or fluctuating, proceed to check connections and cables.

Step 2: Inspect Main Power Relay and Connections Locate the main power relay in the electrical panel beneath the cab floor. Remove and bench-test the relay for proper contact continuity using an ohmmeter (should show less than 1 ohm resistance across contacts when energized). On used excavators, carefully inspect all harness connectors for green corrosion, burnt pins, or physical damage—particularly the large weatherpack connectors near the ECM mounting location.

Step 3: Check Ground Circuit Integrity Trace the ECM ground wire (typically black or black/yellow) to its frame connection point near the hydraulic pump mounting. Remove the ground bolt, wire-brush both the terminal and frame contact surface to bare metal, and reinstall with electrical contact grease. Perform a voltage drop test: with the key ON, measure between battery negative and ECM ground pin—reading should be less than 0.2V.

Step 4: Test Wiring Harness for Damage Physically inspect the main engine harness where it routes along the right-hand frame rail toward the fuel tank. On used PC210LC-7 models, this harness frequently chafes against metal edges. Look for worn insulation, exposed copper, or heat damage. Use a multimeter to check continuity from the battery disconnect switch through to the ECM power pins—infinite resistance indicates a break in the circuit.

Step 5: ECM and Relay Replacement If all wiring and connections test good, replace the main power relay first (Komatsu part number varies by serial number). Clear codes using Komatsu KOMTRAX diagnostic software or a compatible scan tool and retest. If Code S-8 persists with confirmed good power supply, the ECM internal power circuit may be damaged, requiring ECM replacement or professional repair.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu service manual for your specific serial number and follow all safety procedures. If you're uncomfortable working with electrical systems, seek assistance from a certified Komatsu technician or authorized service center.