Komatsu PC800-7 Fault Code E118: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E118?

Fault Code E118 on the Komatsu PC800-7 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 coolant temperature sensor sending irregular voltage signals outside the manufacturer's specified parameters, typically between 0.5-4.5 volts.

The coolant temperature sensor is critical for the PC800-7's performance because the ECM uses this data to adjust fuel injection timing, control engine warm-up cycles, and prevent overheating damage. When this sensor fails or provides inaccurate readings, the engine may run inefficiently, enter derate mode, or suffer long-term damage from improper temperature management.

Common Symptoms

When Code E118 is active on your PC800-7, operators typically experience:

• Warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Engine entering derate mode with reduced power output (typically 25-40% power reduction)
• Difficulty starting when the engine is cold, or excessive black smoke during warm-up
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Increased fuel consumption due to improper fuel mapping based on faulty temperature data

Potential Causes

The most common technical reasons for E118 on used PC800-7 excavators include:

• Coolant temperature sensor failure due to age, thermal cycling, or internal element degradation
• Wiring harness damage at known rub points near the engine block mounting brackets or along the valve cover
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or coastal environments
• ECM internal circuit failure (less common but possible on high-hour machines)
• Coolant contamination causing sensor element coating or failure
• Ground circuit issues affecting sensor reference voltage

How to Troubleshoot and Fix Code E118

Step 1: Visual Inspection Begin by locating the coolant temperature sensor (typically mounted on the engine block near the thermostat housing). Inspect the wiring harness for obvious damage, chafing, or corrosion. On used excavators, pay special attention to areas where the harness contacts metal surfaces or passes near hot exhaust components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Check voltage supply at the harness connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Circuit Verification Test continuity between the sensor connector and the ECM pins. Check for shorts to ground or power. Inspect connector pins for corrosion or bent terminals—a common issue on older machines. Clean connections with electrical contact cleaner.

Step 4: Component Replacement If sensor resistance is out of specification or wiring shows damage, replace the faulty component using genuine Komatsu parts. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) and perform a test cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult your Komatsu service manual and consider professional diagnostic services for complex electrical issues or if you're unfamiliar with high-voltage systems.