Komatsu PC750SE-7 Fault Code E-24: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E-24?

Fault Code E-24 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 turbocharger components. When E-24 triggers, the machine may enter a protective derate mode to prevent engine damage.

Common Symptoms

When Code E-24 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Reduced engine power or automatic derate to lower RPM ranges (typically 1400-1600 RPM maximum)
• Erratic temperature gauge readings showing unusually high, low, or fluctuating coolant temperatures
• Difficulty starting in cold conditions if the ECM receives false low-temperature signals
• Increased fuel consumption due to improper fuel mapping based on incorrect temperature data

Potential Causes

The most common technical causes for E-24 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 cycling causes brittleness
• Corroded sensor connector pins from coolant leaks or moisture intrusion at the sensor mounting location
• Broken or chafed wires along the harness routing path between the sensor and ECM, particularly where the harness contacts frame members
• ECM internal fault (rare) affecting the temperature input circuit
• Low coolant level causing actual overheating and legitimate sensor readings

How to Troubleshoot and Fix Code E-24

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block (typically on the thermostat housing). Check for coolant leaks, corrosion on the connector, and damaged wiring. On used excavators, examine the wiring harness for rub points against the engine block, frame rails, or hydraulic lines—common wear areas on the PC750SE-7.

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 Komatsu specifications). Test harness continuity from the sensor connector to the ECM connector. Check for short circuits to ground and verify proper voltage supply (typically 5V reference) from the ECM.

Step 3: Component Replacement and Verification If the sensor tests outside specifications or the harness shows damage, replace the faulty component. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor coolant temperature during a full operating cycle to confirm proper readings.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.