Komatsu PC70-8 Fault Code E-20: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code E-20?

Fault Code E-20 on the Komatsu PC70-8 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading. This code is triggered when the Electronic Control Module (ECM) detects voltage signals outside the normal operating range from the coolant temperature sensor, typically between 0.5-4.5 volts.

The coolant temperature sensor is critical for the PC70-8's performance because it directly influences fuel injection timing, engine warm-up cycles, and prevents overheating damage. When this sensor fails or provides incorrect data, the ECM cannot properly regulate engine operations, potentially leading to reduced efficiency or catastrophic engine damage.

Common Symptoms

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

• Warning light illumination on the instrument panel, often accompanied by an audible alarm
• Hard starting conditions, especially during cold weather, as the ECM cannot adjust fuel delivery properly
• Rough idling or poor engine performance due to incorrect fuel-air mixture calculations
• Engine derate mode activation, limiting maximum RPM and hydraulic power output
• Inaccurate temperature gauge readings showing extreme high or low temperatures that don't match actual conditions

Potential Causes

The most common technical causes for E-20 on used PC70-8 excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine block mounting brackets
• Corroded or loose connector pins at the sensor plug, especially on machines with coolant leaks
• ECM internal circuit failure (less common but possible on high-hour machines)
• Damaged sensor ground wire or poor chassis ground connection
• Coolant contamination 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 near the thermostat housing. Check for coolant leaks, corrosion on the connector, and physical damage to the wiring harness. On used excavators, pay special attention to harness routing where it contacts metal edges or moving components.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor 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). Test the harness voltage with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Circuit Verification Check for continuity between the sensor connector and ECM pins. Inspect for short circuits to ground or power. On older machines, corrosion inside connectors is common; clean with electrical contact cleaner and apply dielectric grease.

Step 4: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part to ensure proper ECM communication. After replacement, clear codes using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and verify proper operation through a complete heat cycle.

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.