Komatsu PC750LC-7 Fault Code E-15: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E-15?

Fault Code E-15 on the Komatsu PC750LC-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 temperature monitoring system that protects the Komatsu SAA6D140E-3 engine from overheating damage.

The coolant temperature sensor provides critical data to the ECM for fuel injection timing, engine protection protocols, and hydraulic system performance optimization. When E-15 triggers, the ECM may default to a predetermined temperature value, potentially causing inefficient engine operation or unnecessary derating. For a machine of this size and operating capacity, maintaining accurate temperature monitoring is essential to prevent catastrophic engine failure and ensure optimal hydraulic system performance under heavy loads.

Common Symptoms

When Code E-15 is active on your PC750LC-7, operators typically experience:

• Warning light illumination on the monitor panel with possible audible alarm
• Engine derating or reduced power output as a protective measure
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Difficulty starting in cold conditions due to improper fuel mapping
• Cooling fan running continuously at high speed regardless of actual engine temperature

Potential Causes

The most common technical causes for E-15 on used PC750LC-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 or along the frame rail
• Corroded or loose connector pins at the sensor or ECM connection points (common in machines with 8,000+ hours)
• ECM internal circuit failure affecting the temperature input channel
• Coolant contamination causing sensor element fouling or coating
• Ground circuit issues specific to the sensor return path

How to Troubleshoot and Fix Code E-15

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically driver's side, near the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, examine the wiring harness for chafing against the engine block or frame—a common failure point on this model.

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 68°F). Compare readings against Komatsu specifications in the service manual. Test harness continuity from sensor connector to ECM pin and verify ground circuit integrity (should read less than 5 ohms resistance).

Step 3: Live Data Analysis Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to monitor real-time temperature values. Compare sensor readings with an infrared thermometer measurement of actual coolant temperature. A variance greater than 10°F indicates sensor replacement is necessary.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part (P/N 6732-81-3140 or equivalent). For used machines, always apply dielectric grease to connector pins and secure harness away from heat sources using new tie wraps and protective loom.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750LC-7 service manual and consider professional assistance from certified technicians for complex electrical diagnostics or repairs.