Komatsu PC100-6 Fault Code E318: Complete Diagnostic Guide

What is Komatsu PC100-6 Fault Code E318?

Fault Code E318 on the Komatsu PC100-6 indicates a malfunction in the swing motor solenoid valve circuit, specifically detecting an abnormal voltage or open/short circuit condition in the electrical system controlling swing function.

This code is generated when the Electronic Control Module (ECM) detects irregular electrical signals from the swing motor's proportional solenoid valve. The swing motor solenoid regulates hydraulic fluid flow to control the upper structure's rotation speed and smoothness. For the PC100-6's operational efficiency, this circuit must maintain precise voltage levels (typically 12-24V DC) to ensure responsive swing control. When E318 triggers, the machine's swing performance becomes compromised, directly affecting productivity on job sites.

Common Symptoms

When Code E318 is active, operators typically experience:

• Erratic or sluggish swing movement with inconsistent rotational speed
• Complete loss of swing function in one or both directions
• Warning lamp illumination on the instrument panel (amber or red)
• Jerky or delayed swing response when operating the control lever
• Intermittent swing operation that works momentarily then stops

Potential Causes

The most likely technical reasons for E318 on used PC100-6 excavators include:

• Damaged wiring harness at the swivel joint (upper-lower frame connection point), where constant rotation causes wire fatigue and insulation breakdown
• Corroded electrical connectors on the solenoid valve plug, common in machines operating in wet or coastal environments
• Failed swing motor solenoid valve due to internal coil deterioration or mechanical wear
• Broken or shorted wiring from undercarriage contact points or harness routing near hydraulic lines
• ECM internal fault or poor ground connections at the controller mounting location
• Water intrusion into electrical connectors from damaged seals or cab leaks

How to Troubleshoot and Fix Code E318

Step 1: Visual Inspection Begin by inspecting the swing motor solenoid valve connector for corrosion, oil contamination, or bent pins. On used excavators, check the wiring harness routing through the swivel joint—this is a notorious wear point on the PC100-6. Look for abraded insulation or exposed copper wire.

Step 2: Electrical Testing Using a digital multimeter, measure solenoid coil resistance (typically 10-30 ohms when disconnected). Check for continuity between the ECM connector pins and the solenoid valve terminals. Measure supply voltage at the solenoid connector with ignition on—should read approximately 24V DC. Critical for used machines: test harness continuity while manually rotating the upper structure to identify intermittent breaks.

Step 3: Component Testing With the Komatsu diagnostic software (KOMTRAX or PC-compatible tool), perform active solenoid tests to command valve operation. If electrical values are correct but the valve doesn't respond, replace the swing motor solenoid valve assembly. Before installing new parts, clean all ground points on the swing motor housing and apply dielectric grease to connectors.

Step 4: Harness Repair For older PC100-6 units, inspect the center joint harness for damage. This often requires partial disassembly of the swivel housing. Replace any compromised sections with proper gauge wire and heat-shrink connections. Secure routing away from moving components.

Disclaimer: This guide provides general diagnostic procedures. Complex electrical issues may require factory diagnostic tools and trained technicians. Always consult Komatsu service manuals and qualified professionals for critical repairs.