Komatsu PC750SE-7 Fault Code E202: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E202?

Fault Code E202 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 PC750SE-7, the coolant temperature sensor plays a critical role in engine management, controlling fuel injection timing, idle speed, and triggering cooling fan operation. When this sensor fails or sends erratic signals, the ECM cannot properly regulate engine temperature, potentially leading to overheating, reduced performance, or engine protection mode activation.

Common Symptoms

When Code E202 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel with E202 displayed
• Engine derate mode activated, limiting power output to 70-80% capacity
• Cooling fan running continuously at high speed, even when engine is cold
• Rough idle or difficulty starting when engine is warm
• Inaccurate temperature gauge readings showing extreme high or low temperatures

Potential Causes

The most common technical causes for E202 on used PC750SE-7 excavators include:

• Coolant temperature sensor failure due to age-related degradation or internal short circuit
• Damaged wiring harness near the engine block where vibration causes wire chafing (common failure point on this model)
• Corroded or loose connector pins at the sensor plug, especially on machines operating in wet or corrosive environments
• ECM internal fault affecting the sensor input circuit (less common)
• Coolant contamination causing sensor element coating and false readings
• Poor ground connection at the sensor mounting point due to rust or paint buildup

How to Troubleshoot and Fix Code E202

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block near the thermostat housing. Check for physical damage, coolant leaks, or corrosion on the connector pins. On used excavators, pay special attention to harness wear points where wires contact the engine block or frame.

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). Check harness continuity from the sensor connector back to the ECM, looking for opens or shorts to ground.

Step 3: Voltage Signal Check With the sensor connected and ignition on (engine off), backprobe the signal wire at the connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent, suspect ECM issues or harness damage.

Step 4: Connector and Ground Verification Clean all connector terminals with electrical contact cleaner and apply dielectric grease. Verify the sensor has a solid ground by checking continuity between the sensor body and battery negative terminal (should read less than 1 ohm).

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Komatsu part (Part #6732-81-3110 or equivalent). For used machines, always replace the connector pigtail simultaneously if corrosion is present, as this prevents recurring failures.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex electrical issues or if you lack proper diagnostic equipment.