Komatsu PC750SE-7 Fault Code E-13: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E-13?

Fault Code E-13 on the Komatsu PC750SE-7 indicates a malfunction in the engine controller (ECM) communication circuit or a failure in the main relay system. This code specifically relates to power supply irregularities or communication breakdowns between the engine control module (ECM) and the machine's electrical system.

This fault is critical because the PC750SE-7's advanced electronic control system relies on continuous, stable communication between the ECM and various sensors to optimize fuel injection, hydraulic performance, and emissions control. When E-13 triggers, the machine may enter a protective derate mode or experience complete shutdown to prevent potential engine damage.

Common Symptoms

When Code E-13 is active, operators typically experience:

• Warning light illumination on the monitor panel with possible error message display
• Intermittent or complete engine shutdown, particularly during startup or under load
• Loss of hydraulic power or sluggish response in boom, arm, or bucket functions
• Erratic engine RPM or failure to reach full throttle
• Inability to start the machine, with the starter engaging but engine not firing

Potential Causes

The most common technical causes for E-13 on used PC750SE-7 excavators include:

• Main relay failure due to contact wear or coil degradation (common after 8,000+ operating hours)
• Corroded or loose connections at the ECM harness connector (especially pins related to power supply)
• Damaged wiring harness near the battery box or along the right-side frame rail where rubbing against metal edges occurs
• Faulty ECM power supply circuit, including blown fuses or damaged fusible links
• Battery voltage irregularities (weak batteries or failing alternator causing voltage drops below 22V on 24V systems)
• ECM internal failure (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code E-13

Step 1: Verify Power Supply and Battery Condition Using a multimeter, check battery voltage with the key off (should read 24-26V) and during cranking (shouldn't drop below 22V). Inspect battery terminals and cables for corrosion or looseness. Test the alternator output with the engine running (should maintain 27-29V).

Step 2: Inspect Main Relay and Fuses Locate the main relay in the electrical box near the battery compartment. Check for clicking sound when key is turned on. Test relay coil resistance (typically 70-90 ohms) and contact continuity. Inspect all ECM-related fuses and fusible links for damage.

Step 3: Examine ECM Harness and Connections Thoroughly inspect the ECM connector (typically a large multi-pin connector) for bent pins, corrosion, or moisture intrusion. On used excavators, pay special attention to harness routing near the hydraulic tank and along frame rails where abrasion wear commonly occurs. Check for proper ground connections at the ECM mounting points.

Step 4: Perform Diagnostic Software Analysis Connect Komatsu KOMTRAX or compatible diagnostic software to read detailed fault parameters, including voltage readings and communication status. This can pinpoint whether the issue is power-related or communication-specific.

Step 5: Test and Replace Components If all connections and power supply check out, test the main relay by substitution. If the relay is functional, the ECM itself may require replacement or professional reprogramming.

For used excavators, always clean and apply dielectric grease to all connectors during reassembly to prevent future corrosion issues.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance for complex electrical diagnostics or ECM replacement.