Komatsu PC750-7 Fault Code E-15: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E-15?

Fault Code E-15 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.

This fault is critical for the PC750-7's performance because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, engine protection protocols, and hydraulic system efficiency. When E-15 triggers, the engine may enter a protective derate mode to prevent overheating damage, significantly impacting productivity on job sites.

Common Symptoms

When Code E-15 is active on your Komatsu PC750-7, operators typically experience:

• Engine warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Reduced engine power or automatic derate mode activation, limiting maximum RPM
• Erratic temperature gauge readings that fluctuate abnormally or show unrealistic values
• Hard starting conditions, especially during cold weather operation
• Increased fuel consumption due to improper fuel mapping from incorrect temperature data

Potential Causes

The most common technical reasons for E-15 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
• Coolant contamination causing sensor element fouling or coating
• ECM internal fault (rare, but possible in high-hour machines)
• Intermittent short circuits in the sensor wiring due to harness chafing against frame components

How to Troubleshoot and Fix Code E-15

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage, abrasion, or melted insulation. On used excavators, check for harness rub points where cables contact metal surfaces—a common failure point on the PC750-7.

Step 2: Electrical Testing Disconnect the sensor connector and use a multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Also check for voltage supply from the ECM—typically 5 volts reference voltage on the signal wire.

Step 3: Connector and Ground Verification Inspect connector pins for corrosion or bent terminals. Clean with electrical contact cleaner and apply dielectric grease. Verify ground circuit continuity between the sensor ground and ECM ground—resistance should be less than 1 ohm.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part. For used machines, simultaneously inspect coolant condition and flush if contaminated. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and perform a test cycle.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional technician assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.