Komatsu PC750SE-7 Fault Code E315: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E315?

Fault Code E315 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 this sensor fails or sends erratic signals, the ECM cannot properly regulate engine temperature, potentially leading to overheating, reduced performance, or engine protection mode activation.

Common Symptoms

When Code E315 is active, operators typically experience:

• Warning light illumination on the instrument panel, specifically the engine or coolant temperature indicator
• Engine derate mode where power output is automatically reduced to prevent damage
• Erratic temperature gauge readings that fluctuate abnormally or show unrealistic values
• Hard starting conditions, especially in cold weather, due to incorrect fuel mixture calculations
• Increased fuel consumption as the ECM defaults to rich fuel settings without accurate temperature data

Potential Causes

The most common technical causes for E315 in used PC750SE-7 excavators include:

• Coolant temperature sensor failure due to age, corrosion, or internal element degradation
• Wiring harness damage at known rub points near the engine block or along the frame rail
• Corroded or loose connector pins at the sensor or ECM connection points
• Shorted or open circuits in the sensor signal wire or ground circuit
• ECM internal fault (less common) affecting the temperature input circuit
• Coolant contamination causing sensor element coating or failure

How to Troubleshoot and Fix Code E315

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 the connector terminals. On used excavators, examine the entire wiring harness for wear points, especially where it contacts metal surfaces or passes through grommets.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at various temperatures (consult Komatsu specifications, typically 2,000-3,000 ohms at 20°C). Test the signal wire voltage from the ECM with the sensor disconnected—it should read approximately 5 volts. Check ground circuit continuity to ensure less than 1 ohm resistance.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the faulty component. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and perform a test cycle to verify the repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional technician assistance for complex electrical diagnostics.