Komatsu PC750LC-7 Fault Code E206: Complete Diagnostic Guide

What is Komatsu PC750LC-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 outside the manufacturer's specified parameters to the ECM.

In the Komatsu PC750LC-7, the coolant temperature sensor plays a critical role in engine management. The ECM relies on accurate temperature data to optimize fuel injection timing, control engine speed, and prevent overheating damage to the SAA6D140E-3 engine. When this sensor circuit fails, the engine may enter protective derate mode, significantly impacting machine productivity and potentially causing long-term engine damage if ignored.

Common Symptoms

When Code E206 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with E206 displayed
• Reduced engine power or automatic derate to protect against 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 conditions or rough idle during warm-up

Potential Causes

The most common technical causes for E206 on used PC750LC-7 excavators include:

• Faulty coolant temperature sensor due to internal resistance drift or element failure (common after 8,000+ operating hours)
• Damaged wiring harness between the sensor and ECM, particularly at rub points near the engine block or frame rails
• Corroded or loose electrical connectors at the sensor or ECM interface, especially in machines exposed to harsh environments
• Low coolant level causing sensor exposure to air rather than coolant
• ECM internal fault (less common) affecting the sensor input circuit
• Aftermarket sensor incompatibility if previously replaced with non-OEM parts

How to Troubleshoot and Fix Code E206

Step 1: Visual Inspection Begin by checking coolant level in the radiator and overflow tank. Inspect the coolant temperature sensor (typically located on the engine block near the thermostat housing) for physical damage, coolant leaks, or corrosion. On used excavators, carefully examine the wiring harness from sensor to ECM for chafing, cuts, or heat damage—common wear points include areas where harnesses contact the engine block or frame.

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 typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Test harness continuity from sensor connector to ECM pins, checking for opens or shorts to ground. Measure voltage supply from the ECM (usually 5V reference voltage) at the disconnected harness connector.

Step 3: Component Replacement and Verification If sensor resistance is out of specification or harness shows damage, replace the faulty component with genuine Komatsu parts. Clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then run the engine through temperature cycles to verify proper operation.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. Complex electrical issues should be diagnosed by certified Komatsu technicians with proper diagnostic equipment.