Komatsu PC750SE-7 Fault Code E206: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E206?

Fault Code E206 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 sensor sending irregular voltage signals or detecting temperatures outside the normal operating parameters for the Komatsu SAA6D140E-7 engine.

This fault is critical because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, control engine protection systems, and manage the cooling fan operation. When E206 triggers, the engine may enter a protective derate mode to prevent overheating damage, significantly impacting machine productivity and potentially causing costly engine repairs if ignored.

Common Symptoms

When Code E206 is active on your PC750SE-7, operators typically experience:

• Engine warning light illuminated on the monitor panel with reduced engine power
• Automatic engine derate limiting RPM to approximately 1,400-1,600 range
• Cooling fan running continuously at high speed regardless of actual temperature
• Erratic temperature gauge readings or gauge stuck at maximum/minimum positions
• Hard starting conditions when the engine is cold due to incorrect fuel mapping

Potential Causes

The most common technical reasons for E206 on used PC750SE-7 excavators include:

• Coolant temperature sensor failure due to internal element degradation (common after 8,000+ 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 sensor input circuit (less common but possible in high-hour machines)
• Contaminated coolant causing sensor element coating and false readings
• Poor ground connection at the sensor circuit ground point on the engine block

How to Troubleshoot and Fix Code E206

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the left side of the engine block near the thermostat housing. Check for coolant leaks, corrosion on the connector pins, and physical damage to the wiring harness. On used excavators, pay special attention to harness wear points where cables contact 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. Check the harness voltage with the key on, engine off—you should see approximately 5 volts reference voltage from the ECM. Test for continuity between sensor ground and chassis ground.

Step 3: Signal Testing and Verification Connect Komatsu KOMTRAX diagnostic software or 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°F indicates sensor replacement is necessary.

Step 4: Repair and Clear Code Replace the faulty coolant temperature sensor using OEM Komatsu parts (part number 6754-81-6210 or equivalent). Apply dielectric grease to connector pins to prevent future corrosion. If harness damage is found, repair using heat-shrink solder connections rather than crimp connectors. Clear the fault code using diagnostic software and perform a test run under load.

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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 from certified Komatsu technicians for complex electrical diagnostics or if you're uncertain about any procedure.