Komatsu PC750LC-7 Fault Code E-13: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E-13?

Fault Code E-13 on the Komatsu PC750LC-7 indicates a malfunction in the engine controller (ECM) communication circuit or a failure in the main power supply voltage to the controller. This code specifically relates to abnormal voltage detection within the ECM's internal monitoring system, typically triggered when supply voltage falls outside the acceptable range of 20-32 volts DC.

This fault is critical for the PC750LC-7 because the engine control module governs fuel injection timing, turbocharger boost control, and emission system management. When E-13 activates, the machine may enter a protective derate mode to prevent potential engine damage, significantly impacting jobsite productivity and operational efficiency.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel, often accompanied by audible alarm
• Sudden power loss or engine operating in reduced power (derate) mode, limiting maximum RPM to 1,200-1,500
• Intermittent engine stalling, particularly during cold starts or high electrical load conditions
• Monitor display showing abnormal voltage readings or complete loss of digital readouts
• Difficulty starting the engine, with extended cranking times or failure to achieve ignition

Potential Causes

The most common technical causes for E-13 on used PC750LC-7 excavators include:

• Battery system degradation: Weak batteries (below 24V under load) or corroded battery terminals causing voltage drops
• Alternator failure: Insufficient charging output (below 26V at operating RPM) or faulty voltage regulator
• Main power harness damage: Wire chafing at known rub points near the engine mount brackets or along the right-side frame rail
• ECM connector corrosion: Moisture intrusion in the 58-pin ECM connector (located behind the cab), causing high resistance
• Ground circuit failure: Deteriorated ground straps between engine block and frame, common in machines exceeding 8,000 operating hours

How to Troubleshoot and Fix Code E-13

Step 1: Verify Battery and Charging System Using a digital multimeter, measure battery voltage with engine off (should read 24-26V) and running (should read 27-29V). Load test batteries individually; replace if capacity falls below 80%. Inspect all battery cable connections for corrosion and ensure tight connections with proper torque (35-40 ft-lbs).

Step 2: Inspect ECM Power Supply Circuit Locate the main power relay in the electrical box behind the operator's seat. Check for proper voltage at relay output (Pin 87) with key on. Trace the power harness from relay to ECM, inspecting for damaged insulation, particularly where harness passes through bulkhead grommets—a known wear point on used machines.

Step 3: Test ECM Connector and Grounds Disconnect the ECM connector and inspect pins for corrosion or bent contacts. Measure resistance between ECM ground pins and chassis ground (should be less than 1 ohm). Clean all ground connection points with wire brush and apply dielectric grease. If voltage supply tests normal but code persists, ECM replacement may be necessary—consult Komatsu KOMTRAX diagnostic software for internal fault memory.

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