What is Komatsu PC240LC-8 Fault Code E-20?

Fault Code E-20 on the Komatsu PC240LC-8 indicates a malfunction in the engine coolant temperature sensor circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, either reading excessively high (open circuit) or abnormally low (short circuit) compared to standard operating parameters.

The coolant temperature sensor plays a critical role in the PC240LC-8's SAA6D107E-1 engine management system. It sends real-time temperature data to the ECM, which adjusts fuel injection timing, idle speed, and cooling fan operation accordingly. When this sensor circuit fails, the ECM cannot properly regulate engine temperature, potentially leading to overheating, poor fuel efficiency, or excessive emissions. For used excavators, this code often signals aging electrical components or environmental damage accumulated over thousands of operating hours.

Common Symptoms

• Check Engine Light illuminated on the instrument panel with E-20 displayed on the monitor
• Engine running in derated mode with reduced power output to prevent potential damage
• Cooling fan running continuously at high speed, regardless of actual engine temperature
• Difficulty starting the engine when cold, or rough idle during warm-up periods
• Inaccurate temperature gauge readings, showing either constant cold or excessively hot readings

Potential Causes

The most frequent causes of Code E-20 on used PC240LC-8 excavators include:

• Faulty coolant temperature sensor due to internal element degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connection points near the engine block where vibration and heat cause wear
• Loose or oxidized electrical connectors at the sensor plug or ECM terminals—especially problematic in machines operated in wet or corrosive environments
• Coolant contamination on sensor terminals causing false resistance readings
• ECM internal circuit failure (rare, but possible in high-hour machines with electrical system stress)

How to Troubleshoot and Fix Code E-20

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage—chafing, cracking, or melted insulation. On used excavators, pay special attention to areas where harnesses contact metal edges or hot exhaust components. Check the connector terminals for corrosion, bent pins, or coolant intrusion.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance. At room temperature (68°F/20°C), resistance should read approximately 2.3-2.7 kΩ; at operating temperature (176°F/80°C), it should drop to around 0.3-0.4 kΩ. Compare readings to Komatsu specifications in the service manual. Additionally, check for continuity in the wiring between the sensor connector and ECM pins—resistance should be less than 1 ohm.

Step 3: Voltage Signal Verification With the sensor connected and ignition ON (engine OFF), measure voltage at the ECM connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent, the ECM may have internal issues. For used machines, also check ground circuit integrity, as poor grounds frequently cause intermittent sensor codes.

Step 4: Component Replacement and Verification If testing confirms sensor failure, install a genuine Komatsu replacement sensor (Part# 6261-81-6510 or equivalent). After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. Operate the machine through a complete heat cycle and verify the code does not return.

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