Komatsu PC800SE-8R Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC800SE-8R Fault Code E-20?

Fault Code E-20 on the Komatsu PC800SE-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 temperature monitoring system that protects the engine from overheating damage.

The coolant temperature sensor sends voltage signals to the ECM, which uses this data to regulate fuel injection timing, engine speed, and activate warning systems. On the PC800SE-8R's SAA6D170E-5 engine, maintaining accurate temperature readings is critical for preventing catastrophic engine damage and ensuring optimal hydraulic system performance. When this sensor circuit fails, the ECM cannot properly manage engine protection protocols, potentially leading to severe overheating or unnecessary derating.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Engine derate mode activated, limiting maximum RPM and reducing hydraulic power output
• Erratic or stuck coolant temperature gauge readings (showing extremely high, low, or frozen values)
• Difficulty starting in cold conditions due to improper fuel management
• Excessive white smoke during startup if the ECM defaults to cold-start enrichment mode

Potential Causes

The most common technical failures triggering E-20 on used PC800SE-8R excavators include:

• Coolant temperature sensor failure due to age-related degradation or coolant contamination
• Wiring harness damage at known rub points near the engine block mounting brackets
• Corroded or loose connector pins at the sensor plug (common in machines with 5,000+ hours)
• ECM internal circuit failure affecting the sensor input channel
• Shorted or open circuits in the sensor wiring between the engine and cab harness junction
• Contaminated coolant causing sensor element coating and false readings

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 thermostat housing. Check for physical damage, coolant leaks, or corrosion on the connector terminals. On used excavators, examine the wiring harness for abrasion points where it contacts the engine block or frame—this is a common failure point after years of vibration.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM pins, checking for opens or shorts to ground.

Step 3: Live Data Analysis Connect Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live coolant temperature data. Compare the sensor reading against an infrared thermometer measurement of the actual coolant temperature. A variance greater than 10°C indicates sensor replacement is necessary.

Step 4: Connector Service Clean all connector pins with electrical contact cleaner and apply dielectric grease. Many E-20 codes on used machines resolve simply by addressing corroded connections rather than replacing components.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu coolant temperature sensor (Part #6754-81-6210 or equivalent). After installation, clear codes using diagnostic software and perform a test cycle.

---

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 lack proper diagnostic equipment.