Komatsu PC200-7 Fault Code E318: Complete Diagnostic Guide

What is Komatsu PC200-7 Fault Code E318?

Fault Code E318 on the Komatsu PC200-7 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor degradation.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending real-time data to the ECM. This information directly affects fuel injection timing, idle speed control, and engine protection systems. On the PC200-7's SAA6D102E-2 engine, accurate coolant temperature readings are essential for preventing overheating, optimizing combustion efficiency, and triggering appropriate warning systems before catastrophic engine damage occurs.

Common Symptoms

When Code E318 is active, operators typically experience:

• Engine warning lamp illuminated on the instrument cluster with possible audible alarm
• Hard starting conditions, especially in cold weather, due to incorrect fuel enrichment
• Rough idle or erratic engine performance as the ECM defaults to failsafe temperature values
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Reduced engine power or activation of derate mode to protect against potential overheating

Potential Causes

The most common technical reasons for E318 on used PC200-7 excavators include:

• ECT sensor internal failure due to age-related degradation or thermal cycling stress
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the engine mounting brackets
• Corroded or loose electrical connectors at the sensor or ECM terminals (common in machines exposed to moisture)
• Short circuit to ground caused by harness abrasion against the engine block or frame
• ECM internal fault (less common) affecting the sensor input circuit
• Incorrect sensor installation after previous repairs, causing poor thermal contact or electrical grounding issues

How to Troubleshoot and Fix Code E318

Step 1: Visual Inspection Begin by inspecting the ECT sensor located on the engine block (typically near the thermostat housing on the SAA6D102E-2). Check for physical damage, coolant leaks, or corrosion around the sensor body. On used excavators, examine the entire wiring harness from sensor to ECM for chafing, cuts, or worn insulation—pay special attention to areas where the harness contacts metal edges or moving components.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). If readings are infinite (open circuit) or near zero (short circuit), replace the sensor. Also check for continuity between sensor terminals and ground—there should be no continuity.

Step 3: Harness and ECM Circuit Verification With the sensor disconnected, measure voltage at the harness connector (engine side). You should see approximately 5 volts on the signal wire with ignition on. Check for continuity between the harness connector and the ECM pins using a wiring diagram. For used machines, physically inspect connector pins for corrosion, backed-out terminals, or bent contacts—common issues after years of vibration and environmental exposure.

Step 4: System Reset and Verification After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and monitor coolant temperature readings during operation. Verify the temperature rises normally to operating range (82-95°C) and the code does not return.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu PC200-7 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.