Komatsu PC750LC-7 Fault Code E118: Complete Diagnostic Guide

What is Komatsu PC750LC-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 coolant temperature sensor sending irregular voltage signals outside the manufacturer's specified parameters to the ECM.

In the Komatsu PC750LC-7, the coolant temperature sensor plays a critical role in engine management. The ECM relies on accurate temperature data to adjust fuel injection timing, control engine speed, and prevent overheating damage to the SAA6D140E-3 engine. When this sensor circuit fails, the engine may enter protective derate mode, significantly impacting machine productivity and potentially causing long-term engine damage if ignored.

Common Symptoms

When Code E118 is active, operators typically experience:

• Warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Engine derate or reduced power output as the ECM enters protective mode
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Hard starting or rough idle, especially during cold starts
• Increased fuel consumption due to improper fuel mapping from incorrect temperature data

Potential Causes

The most common technical causes for E118 on used PC750LC-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine block or along the chassis rail
• Corroded or loose connector pins at the sensor or ECM connection points (common in machines with high hours)
• ECM internal circuit failure affecting the sensor input channel
• Damaged sensor ground circuit causing voltage reference issues
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code E118

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks, or corrosion. On used excavators, carefully examine the wiring harness for wear points where it contacts the frame or engine components.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor resistance. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Check connector pins for corrosion and ensure proper seating. Measure voltage supply from the ECM (usually 5V reference).

Step 3: Circuit Verification Disconnect the sensor and measure harness continuity to the ECM. Check for shorts to ground or power. For used machines, pay special attention to harness chafing near mounting brackets—a common failure point on high-hour PC750LC-7 units.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor. Clear codes using Komatsu diagnostic software (KOMTRAX) or compatible scan tool. Monitor for code recurrence during operation.

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