Komatsu PC850SE-8R Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC850SE-8R Fault Code E-20?

Fault Code E-20 on the Komatsu PC850SE-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, engine speed, and cooling fan operation. When the sensor provides readings outside the normal operating range (typically -40°F to 300°F), or when a circuit fault is detected, the E-20 code triggers. For the PC850SE-8R's high-performance diesel engine, accurate temperature monitoring is essential to prevent catastrophic engine damage and maintain hydraulic system efficiency.

Common Symptoms

When Code E-20 is active, operators typically experience:

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Engine derate mode activation, limiting power output to 70-80% of normal capacity
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Difficulty starting in cold weather conditions due to improper fuel management
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions

Potential Causes

The most common technical causes for E-20 on used PC850SE-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal stress
• Wiring harness damage at known rub points near the engine block mounting brackets
• Corroded or loose connector pins at the sensor or ECM connection points
• ECM internal circuit failure (less common, but possible in high-hour machines)
• Coolant contamination causing sensor element coating or deterioration
• Ground circuit issues specific to the sensor return path

How to Troubleshoot and Fix Code E-20

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's coolant passage. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, pay special attention to harness wear where wiring contacts the engine or frame—this is a common failure point on the PC850SE-8R.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Check voltage supply at the sensor connector with the key on, engine off—you should see approximately 5 volts. Inspect ground continuity between the sensor ground pin and chassis ground (should be less than 1 ohm).

Step 3: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to monitor live sensor data. Compare actual coolant temperature (use an infrared thermometer) against ECM-reported values. A variance greater than 10°F indicates sensor failure. Check for intermittent connections by wiggling harnesses while monitoring data.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu OEM sensor to ensure proper calibration. Clean all connector contacts with electrical contact cleaner and apply dielectric grease. For used machines, consider replacing the entire sensor pigtail harness if wiring shows any signs of heat damage or brittleness.

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