Komatsu PC750SE-7 Fault Code E-23: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E-23?

Fault Code E-23 on the Komatsu PC750SE-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-5 engine from overheating damage.

The coolant temperature sensor provides critical data to the ECM, which uses this information to regulate fuel injection timing, engine speed limits, and activate warning systems. On the PC750SE-7, this sensor is essential for maintaining optimal engine performance and preventing catastrophic thermal damage to cylinder heads, gaskets, and pistons. When E-23 triggers, the machine may enter a protective derate mode to prevent engine damage.

Common Symptoms

When Code E-23 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with temperature-related alerts
• Reduced engine power or automatic derate limiting machine performance to 70-80% capacity
• Inaccurate temperature gauge readings showing extremely high, low, or erratic coolant temperatures
• Difficulty starting in cold conditions if the ECM receives false low-temperature signals
• Audible warning alarms accompanied by flashing temperature indicators on the display

Potential Causes

The most common technical causes for E-23 on used PC750SE-7 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 8,000+ operating hours)
• Damaged or corroded wiring harness at connector points, especially near the engine block where heat and vibration cause wear
• Corroded sensor connector pins from coolant leaks or moisture intrusion at the sensor mounting location
• Open or short circuit in the sensor signal wire between the sensor and ECM
• ECM internal fault (rare, but possible in high-hour machines with electrical system history)
• Low coolant level causing actual overheating and legitimate sensor readings

How to Troubleshoot and Fix Code E-23

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (located on the engine block near the thermostat housing) for physical damage, coolant leaks, or corrosion. On used excavators, examine the wiring harness for rub points against the engine block, cracked insulation, or signs of previous repairs.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult Komatsu service manual for exact specifications). Check for continuity in the wiring from sensor to ECM connector. Measure voltage supply at the sensor connector with ignition on—should read approximately 5 volts.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the faulty component. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. Clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then operate the machine through a full heat cycle to verify the repair.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional technician assistance for complex electrical diagnostics or ECM-related issues.