Komatsu PC850-8R Fault Code E-24: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code E-24?

Fault Code E-24 on the Komatsu PC850-8R 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 monitoring system, which is critical for preventing engine overheating and maintaining optimal operating temperatures.

The ECM continuously monitors signals from the coolant temperature sensor to regulate fuel injection timing, fan speed, and engine protection protocols. When the sensor voltage falls outside the manufacturer's specified range (typically 0.5-4.5V), or when the temperature reading exceeds safe parameters, the system triggers E-24. For the PC850-8R's SAA6D170E-5 engine, proper coolant temperature monitoring is essential for maintaining the 400+ horsepower output and preventing catastrophic engine damage in demanding mining and quarry applications.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with audible alarm
• Reduced engine power or automatic derate mode to protect the engine from thermal damage
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Cooling fan running continuously at high speed, even during cold starts
• Difficulty starting the engine, particularly in cold weather conditions

Potential Causes

The most common technical causes for E-24 on used PC850-8R 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 insulation breakdown
• Corroded sensor connector pins from coolant leaks or moisture intrusion in the engine compartment
• Low coolant level causing inaccurate temperature readings or air pockets near the sensor
• ECM internal fault or corrupted calibration data (less common but possible in high-hour machines)
• Broken or chafed wires at known rub points between the sensor and ECM, particularly along the engine valley harness routing

How to Troubleshoot and Fix Code E-24

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) and its wiring harness for obvious damage, corrosion, or coolant contamination. On used excavators, pay special attention to harness routing where it contacts hot engine surfaces or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Check for continuity in the wiring from sensor to ECM, and verify ground circuit integrity (should read less than 1 ohm resistance).

Step 3: Sensor Signal Verification With the sensor connected and ignition on (engine off), use Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live sensor voltage. It should read between 3-4V when cold. If voltage is outside this range despite correct resistance readings, inspect for voltage drop in the harness or ECM power supply issues.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part (P/N 6261-81-6510 or equivalent) to ensure proper calibration. Clean connector terminals with electrical contact cleaner and apply dielectric grease before reconnection. After replacement, clear codes using diagnostic software and perform a cold-to-operating temperature test cycle to verify proper operation.

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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.