Komatsu PC750LC-7 Fault Code E112: Complete Diagnostic Guide

What is Komatsu PC750LC-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 temperature monitoring system that protects the Komatsu SAA6D140E-5 engine from overheating damage.

The coolant temperature sensor sends voltage signals to the ECM, which uses this data to regulate fuel injection timing, fan speed, and engine protection protocols. On the PC750LC-7, this sensor is critical because the machine's hydraulic system performance and engine longevity depend on maintaining optimal operating temperatures. When E112 triggers, the ECM may activate protective derate modes to prevent catastrophic engine damage.

Common Symptoms

When Code E112 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with possible audible alarm
• Reduced engine power or automatic derate to protect components from thermal damage
• Cooling fan running continuously at maximum speed regardless of actual temperature
• Erratic temperature gauge readings or gauge stuck at maximum/minimum positions
• Difficulty starting when the engine is cold due to incorrect fuel mapping

Potential Causes

The most common technical causes for E112 on used PC750LC-7 excavators include:

• Faulty coolant temperature sensor due to internal resistance drift (common after 8,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the thermostat housing
• Damaged wiring harness from rubbing against engine components or heat exposure in the sensor circuit
• Low coolant level causing air pockets that prevent accurate temperature sensing
• ECM internal fault or corrupted calibration data (less common but possible in high-hour machines)
• Aftermarket sensor installation with incorrect resistance specifications

How to Troubleshoot and Fix Code E112

Step 1: Visual Inspection Begin by checking coolant level in the radiator and overflow tank. Inspect the sensor connector located on the engine block near the thermostat housing for corrosion, bent pins, or moisture intrusion—common issues in used excavators exposed to harsh environments.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), resistance should read approximately 2,450 ohms (consult your service manual for exact specifications). Check harness continuity from sensor to ECM and verify no shorts to ground.

Step 3: Sensor Replacement and Verification If resistance values are out of specification or the harness shows damage from wear, replace the coolant temperature sensor with a genuine Komatsu part (P/N 6732-81-3140 or equivalent). On used machines, always apply dielectric grease to connector pins to prevent future corrosion. Clear codes using Komatsu diagnostic software (KOMTRAX) and perform a test run.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and seek professional assistance from certified technicians for complex electrical diagnostics or repairs.