Komatsu PC800LC-8R Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code E-20?

Fault Code E-20 on the Komatsu PC800LC-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 PC800LC-8R's SAA6D140E-5 engine, maintaining proper coolant temperature is essential for preventing catastrophic engine damage and ensuring efficient hydraulic system performance.

Common Symptoms

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

• Warning light illumination on the monitor panel with audible alarm
• Engine derate mode activation, limiting power output to 70-80% capacity
• Cooling fan running continuously at high speed regardless of actual temperature
• Difficulty starting in cold conditions or excessive white smoke during warm-up
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions

Potential Causes

The most common technical causes for E-20 on used PC800LC-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal element breakdown
• 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 (common in high-hour machines)
• ECM internal circuit failure affecting the temperature monitoring input channel
• Coolant contamination causing sensor element coating or reduced heat transfer
• Ground circuit issues in the sensor return path to the ECM

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 around the sensor base, and examine the wiring harness for chafing, particularly where it routes near engine mounts. On used excavators, pay special attention to connector corrosion—disconnect and inspect pins for green oxidation or bent terminals.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. With the engine cold, resistance should typically read 2,000-3,000 ohms at 68°F (consult Komatsu specifications for exact values). Test circuit continuity from the sensor connector to the ECM pins. Check for voltage supply from the ECM (usually 5V reference) and verify proper ground circuit integrity (less than 1 ohm resistance).

Step 3: Dynamic Testing and Replacement Connect Komatsu diagnostic software (KOMTRAX Plus) to monitor real-time sensor values. Compare displayed temperature against an infrared thermometer reading of the actual coolant temperature. If readings deviate by more than 10°F, replace the sensor. For used machines, always replace the sensor O-ring and apply anti-seize compound to threads. Clear codes and perform a complete heat cycle test.

Step 4: Advanced Diagnostics If the issue persists after sensor replacement, inspect the ECM connector for moisture intrusion or damaged pins. Test the ECM's 5V reference circuit under load. Consider coolant system contamination—drain and flush if coolant appears degraded, as sensor element coating can cause false readings.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional consultation for complex electrical diagnostics or ECM replacement procedures.