Komatsu PC800SE-7 Fault Code E118: Complete Diagnostic Guide

What is Komatsu PC800SE-7 Fault Code E118?

Fault Code E118 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code specifically relates to the temperature monitoring system that protects the Komatsu SAA6D140E-7 engine from overheating damage.

The coolant temperature sensor sends voltage signals to the ECM, which uses this data to regulate fuel injection timing, engine speed limits, and activate warning systems. On the PC800SE-7, this sensor is critical because improper temperature readings can trigger unnecessary derate modes or fail to protect the engine during actual overheating conditions, potentially causing catastrophic engine damage in a machine of this size and value.

Common Symptoms

When Code E118 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Engine power derate or automatic shutdown if the ECM interprets dangerously high temperature readings
• Erratic temperature gauge readings that fluctuate abnormally or show maximum temperature immediately at startup
• Cooling fan running continuously at high speed, even when the engine is cold
• Difficulty starting or rough idle conditions due to incorrect fuel mapping based on faulty temperature data

Potential Causes

The most common technical causes for E118 on used PC800SE-7 excavators include:

• Coolant temperature sensor failure due to age, thermal cycling, or internal element degradation (common after 8,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug, particularly where the harness routes near the engine block
• Broken or chafed wires in the sensor circuit caused by vibration or contact with hot engine components
• Faulty ECM ground connections causing voltage reference issues
• Contaminated coolant causing sensor element coating or corrosion
• Previous repair attempts using non-OEM sensors with incorrect resistance specifications

How to Troubleshoot and Fix Code E118

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check the connector for corrosion, moisture, or damaged pins. On used excavators, examine the entire wiring harness for rub points, especially where it contacts the engine or frame—this is a known wear point on PC800 series machines.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test harness continuity from the sensor connector back to the ECM, checking for opens or shorts to ground. Verify supply voltage at the sensor connector (typically 5V reference from the ECM).

Step 3: Component Replacement and Verification If the sensor tests outside specifications or the harness shows damage, replace the faulty component with genuine Komatsu parts. For used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor coolant temperature during a complete warm-up cycle to verify proper operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.