What is Komatsu PC200LC-8 Fault Code E15 CA187?

Fault Code E15 CA187 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the ECT (Engine Coolant Temperature) sensor system. This code is part of Komatsu's proprietary diagnostic system and directly affects the ECM's (Engine Control Module) ability to manage fuel injection timing, idle speed, and engine protection protocols.

For the PC200LC-8 model equipped with the SAA6D107E-1 engine, accurate coolant temperature readings are critical. The ECM relies on this data to prevent overheating, optimize combustion efficiency, and trigger warning systems before catastrophic engine damage occurs. When this sensor circuit fails, the engine may enter a protective derate mode, significantly limiting machine productivity on the job site.

Common Symptoms

• Coolant temperature gauge reading incorrectly (stuck at minimum, maximum, or erratic fluctuations)
• Engine warning light or check engine light illuminated on the monitor panel
• Engine runs rich or exhibits hard starting conditions, especially in cold weather
• ECM defaults to fail-safe mode, causing reduced engine power or RPM limitation
• Radiator cooling fan runs continuously at high speed regardless of actual engine temperature

Potential Causes

The most frequent causes of CA187 in used PC200LC-8 excavators include:

• ECT sensor internal failure due to age-related degradation (common after 5,000+ operating hours)
• Wiring harness damage at known rub points near the engine block mounting brackets or along the right-hand frame rail
• Corroded or loose connector terminals at the sensor plug, particularly from coolant leaks or moisture intrusion
• Open circuit caused by broken wires inside the insulation jacket (not visible externally)
• Failed ECM internal circuitry (rare, but possible in high-hour machines with electrical system surges)
• Incorrect sensor replacement with non-OEM parts having wrong resistance curves

How to Troubleshoot and Fix Code E15 CA187

Step 1: Visual Inspection Locate the ECT sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for obvious damage, abrasion, or coolant contamination. Check connector pins for corrosion or bent terminals—this is especially critical on used excavators with outdoor storage history.

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 the PC200LC-8 service manual for exact specifications). Test the harness continuity from the sensor connector back to the ECM pins—any reading above 5 ohms indicates excessive resistance.

Step 3: Voltage Signal Check With the ignition on and sensor disconnected, measure reference voltage at the harness connector. You should see approximately 5 volts DC. If voltage is absent, trace the power supply circuit for breaks or check ECM fuse integrity.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, install a genuine Komatsu ECT sensor (Part #6754-81-6120 or equivalent). For used machines, always apply dielectric grease to connector terminals before reassembly. Clear the fault code using Komatsu diagnostic software (KOMTRAX Plus) or a compatible J1939 scan tool, then perform a test run monitoring live coolant temperature data.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC200LC-8 service manual and consider professional assistance from certified Komatsu technicians for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.