KomatsuPC750LC-7 Fault Code E-24: Complete Diagnostic Guide

What is KomatsuPC750LC-7 Fault Code E-24?

Fault Code E-24 on the Komatsu PC750LC-7 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition.

This diagnostic trouble code is triggered when the Engine Control Module (ECM) receives voltage readings outside the normal operating parameters (typically above 4.9V) from the coolant temperature sensor. The sensor, a negative temperature coefficient (NTC) thermistor, is critical for proper fuel injection timing, cold-start enrichment, and cooling fan activation.

On the PC750LC-7's SAA6D140E-3 engine, accurate coolant temperature readings are essential for maintaining optimal combustion efficiency and preventing thermal damage to critical components.

Common Symptoms

• Warning indicator illuminates on the monitor panel with E-24 displayed
• Engine may enter derate mode, limiting power output and hydraulic performance
• Cooling fans may run continuously at maximum speed regardless of actual temperature
• Poor cold-start performance and rough idle conditions
• Inaccurate or erratic temperature gauge readings on the operator display
• Increased fuel consumption due to improper fuel mixture calculations

Potential Causes

• Coolant temperature sensor failure — internal thermistor degradation common in high-hour machines
• Open circuit in the sensor wiring harness due to chafing or rodent damage
• Corroded connector pins at the sensor or ECM connection points
• Damaged wiring near the exhaust manifold from heat exposure
• ECM ground circuit issues affecting sensor signal interpretation
• Previous improper repairs or spliced wiring from past owners

How to Troubleshoot and Fix Code E-24

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block near the thermostat housing. Inspect the wiring harness for visible damage, particularly where it routes near hot exhaust components. On used excavators, check for evidence of previous repairs, abraded insulation, or corroded terminals.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At 20°C (68°F), expect approximately 2.5-3.0 kΩ. An open-loop reading (OL) confirms sensor failure. Additionally, verify 5V reference voltage and proper ground continuity at the harness connector using Komatsu VHMS diagnostic software.

Step 3: Connector and Harness Repair Clean all connector pins with electrical contact cleaner. If corrosion is present, replace the connector. For used equipment, apply dielectric grease to prevent future moisture intrusion. Replace the sensor if resistance values are out of specification.

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Disclaimer: This guide is for informational purposes only. Always consult official Komatsu service documentation and qualified heavy equipment technicians for diagnosis and repairs on your specific machine.