KomatsuPC750LC-7 Fault Code E-23: Complete Diagnostic Guide

What is KomatsuPC750LC-7 Fault Code E-23?

Fault Code E-23 on the Komatsu PC750LC-7 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high or open circuit condition.

This diagnostic trouble code is triggered when the Engine Control Module (ECM) receives voltage readings outside the normal operating parameters from the coolant temperature sensor. On the PC750LC-7's SAA6D140E-3 engine, this sensor provides critical data for fuel injection timing, cooling fan activation, and cold-start enrichment calculations.

When E-23 is active, the ECM cannot accurately monitor engine temperature, potentially leading to overheating damage or inefficient combustion. For a machine of this size class, ignoring this code risks catastrophic engine failure.

Common Symptoms

• Warning indicator illuminates on the monitor panel with audible alarm
• Engine may enter derate mode, limiting power output and hydraulic performance
• Erratic or non-functional temperature gauge readings
• Cooling fan running continuously at maximum speed (failsafe mode)
• Rough idle or poor cold-start performance

Potential Causes

The most frequent causes of E-23 on used PC750LC-7 units include:

• Coolant temperature sensor failure due to thermal cycling degradation
• Wiring harness damage near the sensor connector, particularly where it routes past the turbocharger
• Corroded connector pins from coolant contamination or environmental exposure
• Open circuit in the signal wire between sensor and ECM
• ECM ground fault affecting sensor reference voltage

On high-hour machines, inspect the harness routing carefully—the PC750LC-7 is known for chafing issues where wiring contacts the engine block near cylinder six.

How to Troubleshoot and Fix Code E-23

Step 1: Visual Inspection Locate the coolant temperature sensor on the engine block. Inspect the connector for corrosion, moisture intrusion, or damaged pins. Check the harness for abrasion, particularly along heat-exposed routing paths.

Step 2: Electrical Testing Using a multimeter, measure resistance across the sensor terminals. At 20°C (68°F), expect approximately 2.5-3.0 kΩ. At operating temperature (80°C), resistance should drop to 300-350 ohms. Infinite resistance indicates an open sensor.

Step 3: Circuit Verification With the connector disconnected, verify 5V reference voltage from the ECM using Komatsu VHMS diagnostic software or a multimeter. Test continuity between the sensor connector and ECM pins to isolate harness breaks.

Step 4: Component Replacement If testing confirms sensor failure, replace with OEM-specification components. On used excavators, always clean connector terminals with electrical contact cleaner and apply dielectric grease before reassembly.

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Disclaimer: This guide is for informational purposes only. Always consult qualified heavy equipment technicians and reference official Komatsu service documentation before performing repairs.