Komatsu PC850-8R Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC850-8R Fault Code E-20?

Fault Code E-20 on the Komatsu PC850-8R 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, fan speed, and engine protection protocols. When the sensor provides readings outside the normal operating range (typically -40°F to 300°F), or when circuit voltage falls outside specified parameters (usually 0.5V to 4.5V), the system triggers E-20. For the PC850-8R's SAA6D170E-5 engine, proper temperature monitoring is essential for protecting the high-pressure fuel system and preventing catastrophic engine damage.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel with audible alarm
• Cooling fan running continuously at maximum speed regardless of actual engine temperature
• Engine derate mode activated, limiting power output to 70-80% capacity to prevent potential overheating
• Erratic temperature gauge readings showing unusually high, low, or fluctuating temperatures
• Difficulty starting in cold conditions if the ECM receives false low-temperature signals

Potential Causes

The most common technical causes for E-20 on used PC850-8R excavators include:

• Coolant temperature sensor failure due to internal element degradation (common after 8,000+ operating hours)
• Corroded or loose connector pins at the sensor harness connection point near the thermostat housing
• Damaged wiring harness from rubbing against the engine block or exhaust components—particularly at the routing point behind the fuel filter assembly
• ECM internal fault affecting the temperature sensor input circuit (rare but possible in high-hour machines)
• Low coolant level causing intermittent sensor exposure and false readings
• Contaminated coolant creating electrical conductivity issues affecting sensor accuracy

How to Troubleshoot and Fix Code E-20

Step 1: Visual Inspection Begin by checking coolant level in the expansion tank and radiator. Inspect the coolant temperature sensor (located on the engine block near the thermostat housing) and its connector for corrosion, oil contamination, or physical damage. On used excavators, carefully examine the wiring harness routing for wear points, especially where it contacts metal surfaces.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult your service manual for exact specifications). Check circuit voltage at the harness connector with ignition on—you should see approximately 5V reference voltage from the ECM.

Step 3: Circuit Verification Test for continuity between the sensor connector and ECM pins (typically E2-31 and E2-32 on the PC850-8R). Resistance should be less than 5 ohms. Check for short circuits to ground by measuring resistance between each wire and chassis ground (should read infinite resistance).

Step 4: Component Replacement If sensor resistance is out of specification or circuit testing reveals wiring damage, replace the faulty component. For used excavators with over 10,000 hours, consider replacing both the sensor and connector as preventive maintenance. After repairs, clear codes using Komatsu KOMTRAX diagnostic software or a compatible scan tool and verify proper operation.

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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.