Komatsu PC750-7 Fault Code E118: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E118?

Fault Code E118 on the Komatsu PC750-7 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 voltage signals outside the expected range to the ECM, or the sensor detecting temperatures beyond safe operating parameters.

The coolant temperature sensor is critical for the PC750-7's SAA6D140E-5 engine performance. It directly influences fuel injection timing, engine protection protocols, and hydraulic oil temperature management. When this sensor fails or provides incorrect data, the ECM cannot properly regulate engine operations, potentially leading to overheating, reduced power output, or automatic engine derate modes.

Common Symptoms

When Code E118 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Automatic engine power derate or speed limitation to prevent potential overheating damage
• Erratic temperature gauge readings showing unusually high, low, or fluctuating coolant temperatures
• Difficulty starting in cold conditions if the ECM receives false low-temperature signals
• Increased fan engagement as the system attempts to compensate for perceived high temperatures

Potential Causes

The most common technical causes for E118 on used PC750-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• Damaged wiring harness near the sensor connector, particularly where the harness routes along the engine block (known rub point)
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or corrosive environments
• ECM internal circuit issues affecting the sensor input channel (less common but possible in high-hour machines)
• Coolant contamination causing sensor element coating or actual overheating conditions triggering legitimate warnings

How to Troubleshoot and Fix Code E118

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks around the sensor base, and examine the wiring harness for abrasion, cuts, or heat damage. On used excavators, pay special attention to harness routing where it contacts metal surfaces.

Step 2: Connector and Resistance Testing Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion. Using a digital multimeter, measure the sensor's 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). Compare readings at different temperatures if possible.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on, measure voltage at the ECM-side connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, inspect wiring between the sensor and ECM for breaks or shorts to ground.

Step 4: Sensor Replacement and Verification If the sensor fails resistance testing or the circuit checks are normal but the code persists, replace the coolant temperature sensor with a genuine Komatsu part. After installation, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, and monitor for code recurrence during operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.