Komatsu PC750-7 Fault Code E112: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E112?

Fault Code E112 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 irregular voltage signals outside the manufacturer's specified parameters to the ECM.

The coolant temperature sensor is critical for the PC750-7's performance because it directly influences fuel injection timing, engine protection protocols, and hydraulic oil temperature management. When this sensor fails or provides inaccurate data, the ECM cannot properly regulate engine operations, potentially leading to overheating, reduced power output, or automatic engine shutdown to prevent catastrophic damage.

Common Symptoms

When Code E112 is active on your PC750-7, operators typically experience:

• Warning light illumination on the instrument cluster, specifically the engine malfunction indicator
• Engine derate mode where maximum RPM is limited to protect components
• Difficulty starting or extended cranking times, especially in cold conditions
• Erratic temperature gauge readings that fluctuate abnormally or show incorrect temperatures
• Automatic engine shutdown if the ECM interprets critically high temperature readings

Potential Causes

The most common technical reasons for E112 appearing on used PC750-7 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 8,000+ operating hours)
• Damaged wiring harness near the sensor connector, particularly where the harness routes along the engine block and experiences heat cycling
• Corroded or loose electrical connections at the sensor plug or ECM terminals
• Shorted or open circuits in the sensor signal wire between the sensor and ECM
• Low coolant levels causing intermittent sensor exposure and false readings
• ECM internal fault (less common) affecting the temperature input circuit

How to Troubleshoot and Fix Code E112

Step 1: Visual Inspection Begin by checking coolant levels and inspecting the coolant temperature sensor location (typically on the engine block near the thermostat housing). Examine the wiring harness for obvious damage, chafing against metal surfaces, or heat damage. On used excavators, pay special attention to connector pins for corrosion or bent terminals.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from sensor connector to ECM and check for shorts to ground. Verify supply voltage from the ECM (usually 5V reference).

Step 3: Component Replacement and Verification If sensor resistance is out of specification or harness damage is found, replace the faulty component. For used machines, always apply dielectric grease to connectors to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair.

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