Komatsu PC750SE-7 Fault Code E118: Complete Diagnostic Guide

What is Komatsu PC750SE-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 PC750SE-7, the coolant temperature sensor plays a critical role in engine management, controlling fuel injection timing, idle speed, and triggering cooling system responses. When the ECM cannot accurately monitor engine temperature, it may initiate protective measures that significantly impact machine performance and can lead to costly engine damage if ignored.

Common Symptoms

When Code E118 is active on your PC750SE-7, operators typically experience:

• Engine warning light illuminated on the monitor panel with possible audible alarm
• Hard starting conditions, especially during cold starts or after the machine has cooled down
• Rough idling or inconsistent engine RPM fluctuations
• Reduced engine power or derate mode activation to prevent overheating damage
• Inaccurate coolant temperature readings displayed on the monitor (showing extremely high or low temperatures that don't match actual conditions)

Potential Causes

The most common technical reasons for E118 on used PC750SE-7 excavators include:

• Faulty coolant temperature sensor due to age-related degradation or internal element failure
• Damaged or corroded wiring harness connections at the sensor plug (common wear point near the engine block)
• Broken or frayed sensor wiring caused by vibration, heat exposure, or rubbing against engine components
• Corroded sensor terminals from coolant leaks or moisture intrusion in the connector
• ECM internal fault (less common) affecting the temperature monitoring circuit
• Poor ground connection at the sensor or ECM grounding points

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, abrasion, or corrosion. On used excavators, check for coolant residue around the sensor indicating leaks that may have compromised the electrical connection.

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

Step 3: Harness and Connection Verification Inspect the connector pins for corrosion, bent terminals, or moisture. Clean connections with electrical contact cleaner. Test continuity through the entire harness from sensor to ECM. For used machines, pay special attention to harness routing where it may contact hot engine surfaces or moving components.

Step 4: Component Replacement If the sensor tests outside specifications or the harness shows damage, replace the faulty component with genuine Komatsu parts. After replacement, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and perform a test run to verify the repair.

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