What is Komatsu PC120LC-6 Fault Code E-11?

Fault Code E-11 on the Komatsu PC120LC-6 indicates a malfunction in the engine controller (ECM) communication circuit or a failure in the main relay system. This code specifically points to an interruption in the power supply or signal transmission between the ECM and critical engine control components.

The PC120LC-6 uses a Komatsu SAA4D102E-2 engine with electronic fuel injection management. When E-11 triggers, the ECM loses its ability to properly regulate fuel delivery, monitor sensor inputs, or control actuators. This directly impacts engine performance, fuel efficiency, and emission control. For used excavators, this code often signals aging electrical components or harness degradation rather than catastrophic engine failure.

Common Symptoms

• Engine cranks but fails to start, or starts then immediately shuts down
• Monitor panel displays E-11 code with amber or red warning light illuminated
• Intermittent power loss during operation, particularly when machine vibrates or moves
• Erratic engine RPM or failure to respond to throttle inputs
• Complete loss of electronic functions including monitor display and diagnostic capabilities

Potential Causes

The most frequent causes in used PC120LC-6 excavators include:

• Main relay failure - The relay controlling ECM power supply degrades over time, causing intermittent connection
• Corroded or loose ECM connectors - Moisture intrusion at the 32-pin ECM harness connector (located behind operator seat)
• Damaged wiring harness - Chafing at known rub points near the engine mount brackets and along the right-side frame rail
• Faulty ECM ground connection - Corrosion at ground terminal G101 (frame-mounted near battery box)
• Battery voltage issues - Weak battery or failing alternator causing voltage drops below 10.5V during cranking
• ECM internal failure - Less common, but possible in high-hour machines (8,000+ hours)

How to Troubleshoot and Fix Code E-11

Step 1: Verify Power Supply Using a multimeter, check battery voltage (should read 12.5-13V key off, 13.5-14.5V running). Inspect battery terminals and cables for corrosion. Test the main relay (located in fuse box under operator seat) - it should click audibly when key is turned on and show continuity across terminals 30-87 when energized.

Step 2: Inspect ECM Connections Remove the ECM cover and carefully disconnect the main harness connector. Inspect all pins for corrosion, bent contacts, or moisture. Clean with electrical contact cleaner and apply dielectric grease. Check ground terminal G101 - remove, wire brush both surfaces, and reinstall with star washer.

Step 3: Test Harness Continuity With ECM disconnected, use a multimeter to check continuity between ECM connector pins and the main relay. Pay special attention to the harness routing along the right frame rail where it passes near hydraulic lines - this is a common wear point on used machines. Look for abraded insulation or exposed copper.

Step 4: Monitor Voltage During Cranking Reconnect everything and monitor ECM power supply voltage (Pin 1 at ECM connector) during cranking. Voltage should not drop below 10V. If it does, address battery or starter issues first.

For used excavators, replacing the main relay ($45-80) and thoroughly cleaning all connections resolves E-11 in approximately 70% of cases. If the code persists after electrical verification, ECM replacement may be necessary ($800-1,500 for remanufactured unit).

---

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.