Komatsu PC750-7 Fault Code E-23: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E-23?

Fault Code E-23 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 (also called the water temperature sensor) that monitors engine operating temperature and sends voltage signals to the ECM.

This fault is critical for the PC750-7's performance because the ECM relies on accurate coolant temperature data to control fuel injection timing, engine speed limits, and cooling fan operation. When E-23 triggers, the ECM may default to a predetermined temperature value, potentially causing inefficient combustion, increased fuel consumption, or engine protection mode activation. For used excavators, this sensor circuit is particularly vulnerable to corrosion and wiring degradation after thousands of operating hours.

Common Symptoms

When Code E-23 is active on your PC750-7, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by an audible alarm
• Engine derate or power reduction as the ECM enters protective mode to prevent overheating damage
• Erratic temperature gauge readings that fluctuate abnormally or remain stuck at minimum/maximum positions
• Cooling fan running continuously at high speed, even during cold starts or low-load operations
• Difficulty starting in cold weather conditions due to improper fuel enrichment calculations

Potential Causes

The most common technical causes for E-23 on used PC750-7 excavators include:

• Faulty coolant temperature sensor with internal resistance drift (common after 8,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug, especially where the harness routes near the engine block
• Broken or chafed sensor wires at known rub points between the sensor and ECM connector (check near engine mounts)
• Corroded ECM pins or moisture intrusion in the engine control module connector
• Poor ground connection at the sensor ground circuit or ECM ground points
• Coolant contamination causing sensor element fouling or accelerated corrosion

How to Troubleshoot and Fix Code E-23

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically near the thermostat housing). Check for physical damage, coolant leaks, or corrosion on the sensor body and electrical connector. On used excavators, carefully examine the wiring harness from sensor to ECM for chafing, especially where it contacts metal surfaces or passes through grommets.

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 PC750-7 service manual for exact specifications). Test the harness continuity from the sensor connector to the ECM pins, checking for opens or shorts to ground. Measure supply voltage at the sensor connector with ignition on—you should see approximately 5 volts from the ECM.

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live coolant temperature data. Compare the sensor reading against actual engine temperature using an infrared thermometer. If readings differ by more than 10°F, replace the sensor. Check ECM connector pins for corrosion or bent terminals—a common issue in high-hour used machines. Clean all ground points with electrical contact cleaner and dielectric grease.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor (Part #6732-81-3140 or equivalent). For used excavators, always replace the connector pigtail if any corrosion is present, as this prevents recurring failures. After installation, clear codes using diagnostic software and perform a test cycle to verify proper operation.

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Disclaimer: This guide provides general diagnostic information for Code E-23. Always consult the official Komatsu PC750-7 service manual and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.