Komatsu PC800-7 Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC800-7 Fault Code E-20?

Fault Code E-20 on the Komatsu PC800-7 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 the circuit shows an open or short condition, the E-20 code triggers. For the PC800-7's SAA6D140E-3 engine, maintaining proper coolant temperature monitoring is essential for preventing catastrophic engine damage and ensuring the hydraulic system operates at peak 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 where maximum RPM is limited to protect the engine from potential overheating
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Difficulty starting in cold weather conditions due to incorrect fuel mapping

Potential Causes

The most common technical causes for E-20 on used PC800-7 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 or along the valve cover
• Corroded or loose connector pins at the sensor plug, especially on machines operating in harsh environments
• ECM internal circuit failure affecting the temperature monitoring input (less common)
• Damaged sensor threads causing coolant leaks and sensor exposure to air
• Aftermarket sensor incompatibility if previous repairs used non-OEM parts

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 visible damage, chafing, or melted insulation. Check the connector for corrosion, bent pins, or coolant contamination—a common issue on used excavators with aging seals.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 68°F (20°C), resistance should read approximately 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. Check for short circuits to ground by measuring resistance between each wire and chassis ground (should read infinite resistance).

Step 3: Live Data Analysis Connect Komatsu diagnostic software (KOMTRAX Plus or equivalent) to monitor real-time coolant temperature readings. Compare the displayed temperature against an infrared thermometer reading taken directly on the engine block. A variance greater than 10°F indicates sensor failure.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu sensor (Part #6732-81-3140 or equivalent). For used excavators, always apply dielectric grease to connector pins and inspect the sensor mounting boss for thread damage. Clear codes using diagnostic software and perform a cold-start test cycle to verify repair.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC800-7 service manual and consider professional assistance for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.