What is Komatsu PC110-8M0 Fault Code E-20?

Fault Code E-20 on the Komatsu PC110-8M0 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal engine temperature condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects either an out-of-range signal from the coolant temperature sensor or a reading that exceeds the engine's safe operating parameters.

This code is critical for the PC110-8M0's performance because the ECM relies on accurate coolant temperature data to manage fuel injection timing, idle speed, and engine protection protocols. When E-20 is active, the engine may enter a protective derate mode to prevent catastrophic overheating damage to the cylinder head, gaskets, or piston rings. For used excavators, this code often signals age-related sensor degradation or wiring issues common in machines with over 5,000 operating hours.

Common Symptoms

When Code E-20 is active on your Komatsu PC110-8M0, operators typically experience:

• Engine warning light illuminated on the instrument cluster (amber or red depending on severity)
• Reduced engine power or automatic throttle limitation (derate mode activated)
• Abnormal engine idle or rough running, especially during cold starts
• Coolant temperature gauge showing erratic readings or pegged at maximum
• Hydraulic system sluggishness due to reduced engine RPM capability

Potential Causes

The most common technical causes for Code E-20 on used PC110-8M0 excavators include:

• Faulty coolant temperature sensor (typical failure point after 4,000-6,000 hours)
• Corroded or damaged wiring harness connections at the sensor plug (common vibration wear point near the thermostat housing)
• Open or short circuit in the sensor wiring between the sensor and ECM connector
• Low coolant level causing actual overheating and triggering legitimate high-temperature warnings
• Defective ECM temperature input circuit (rare, but possible in machines exposed to water ingress)
• Aftermarket sensor incompatibility if previous repairs used non-OEM parts

How to Troubleshoot and Fix Code E-20

Step 1: Visual Inspection Begin by checking the coolant level in the radiator and overflow tank when the engine is cold. Inspect the coolant temperature sensor (located near the thermostat housing on the cylinder head) for physical damage, coolant leaks, or corrosion on the electrical connector. On used excavators, carefully examine the wiring harness for chafing against the engine block or fan shroud—a common failure point on the PC110-8M0.

Step 2: Electrical Testing Using a digital multimeter, disconnect the coolant temperature sensor and measure its resistance. At 68°F (20°C), a functioning Komatsu sensor should read approximately 2,500-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity in the wiring harness from the sensor connector to the ECM pins. Inspect for voltage at the sensor connector with the ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If the sensor resistance is out of specification or the wiring shows breaks/shorts, replace the faulty component with a genuine Komatsu part (part number 6261-81-6510 or equivalent). For used machines, apply dielectric grease to connector pins to prevent future corrosion. After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and perform a test run, monitoring live coolant temperature data to confirm proper sensor operation.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC110-8M0 service manual and consider professional evaluation by a certified heavy equipment technician for complex electrical issues or persistent fault codes.