Komatsu PC750SE-7 Fault Code E117: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E117?

Fault Code E117 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 E117 is active on your PC750SE-7, operators typically experience:

• Warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Engine running in derate mode (reduced power output) as a protective measure
• Difficulty starting, especially in cold conditions, or rough idle when the engine is cold
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Inaccurate temperature gauge readings showing extreme high or low temperatures

Potential Causes

The most common technical reasons for E117 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 wires in the sensor circuit caused by vibration or rubbing against engine components
• Corroded ECM connector pins affecting signal transmission
• Low coolant level causing sensor exposure to air instead of coolant
• Failed ECM (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code E117

Step 1: Visual Inspection Begin by checking coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (typically located on the engine block near the thermostat housing) and its wiring harness for obvious damage, corrosion, or loose connections. On used excavators, pay special attention to harness routing where wires may rub against brackets or the engine block.

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

Step 3: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor live sensor data. Compare actual coolant temperature with sensor readings. Check for intermittent connection issues by wiggling the connector while monitoring values. Inspect ECM ground connections for corrosion, as poor grounds frequently cause sensor circuit faults in high-hour machines.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu or OEM-equivalent sensor. Always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear the fault code and perform a test run under load.

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Disclaimer: This guide provides general diagnostic information. Always consult your Komatsu service manual and consider professional assistance for complex electrical diagnostics, especially on used equipment with unknown service history.