Komatsu PC800-8R Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code E-20?

Fault Code E-20 on the Komatsu PC800-8R 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°C to 150°C), or when circuit voltage falls outside specified parameters (usually 0.5V to 4.5V), the system triggers E-20. For the PC800-8R's SAA6D140E-5 engine, proper temperature monitoring is essential to prevent catastrophic engine damage and maintain the machine's 400+ horsepower output efficiently.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with audible alarm
• Engine derate mode activated, limiting maximum RPM and hydraulic performance
• Inaccurate temperature gauge readings showing extremely high or low temperatures
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Difficulty starting in cold conditions or excessive white smoke during warm-up

Potential Causes

The most common technical causes for E-20 on used PC800-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short circuits
• Damaged wiring harness near the engine block where vibration causes wire chafing (common failure point behind the fuel filter assembly)
• Corroded or loose connector pins at the sensor plug, especially on machines operating in harsh environments
• ECM internal fault affecting the temperature monitoring circuit (less common)
• Coolant contamination causing sensor element coating and false readings
• Ground circuit failure in the sensor return path to the ECM

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, or burns. On used excavators, pay special attention to areas where the harness contacts metal surfaces or passes near hot exhaust components. Check the connector for corrosion, bent pins, or coolant intrusion.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across its terminals. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult Komatsu specifications). Test circuit voltage at the harness connector with ignition on: you should see approximately 5V reference voltage from the ECM. Check ground continuity between the sensor ground pin and chassis ground (should be less than 1 ohm).

Step 3: Component Replacement and Verification If sensor resistance is out of specification or the circuit shows voltage irregularities, replace the coolant temperature sensor (Komatsu part number 6732-81-3140 or equivalent). For used machines, always replace the connector pigtail if corrosion is present. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, and verify the code doesn't return after a full heat cycle.

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