Komatsu PC750SE-7 Fault Code E112: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E112?

Fault Code E112 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 E112 is active on your PC750SE-7, operators typically experience:

• Warning light illumination on the instrument cluster, specifically the engine or coolant temperature indicator
• Engine derate mode where power output is significantly reduced to prevent thermal damage
• Erratic temperature gauge readings that fluctuate abnormally or show maximum temperature immediately at startup
• Difficulty starting in cold conditions due to improper fuel enrichment
• Increased fuel consumption as the ECM defaults to safe-mode fuel mapping

Potential Causes

The most common technical reasons for E112 on used PC750SE-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 where vibration causes insulation wear
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or corrosive environments
• ECM internal fault (less common) affecting the temperature sensor input circuit
• Coolant contamination causing sensor element coating and inaccurate readings
• Ground circuit issues creating voltage reference problems

How to Troubleshoot and Fix Code E112

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 visible damage, chafing, or burns. On used excavators, pay special attention to areas where the harness contacts metal surfaces or passes near hot exhaust components. Check the connector for corrosion, bent pins, or moisture intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance at ambient temperature (typically 2,000-3,000 ohms at 20°C for Komatsu sensors, but verify with service manual specifications). Test the harness continuity from the sensor connector back to the ECM. Check for proper ground circuit integrity and measure voltage supply at the sensor connector with ignition on (should read approximately 5 volts).

Step 3: Component Replacement and Verification If resistance values are out of specification or the sensor shows physical damage, replace the coolant temperature sensor with a genuine Komatsu part. 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 monitor for code recurrence during a complete heat cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.