Komatsu PC240LC-10 Fault Code CA2357: Complete Diagnostic Guide

What is Komatsu PC240LC-10 Fault Code CA2357?

Fault Code CA2357 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal from the ECT (Engine Coolant Temperature) sensor to the engine ECM (Engine Control Module). This code triggers when the sensor voltage falls outside the manufacturer's specified range of 0.2-4.8 volts.

The ECT sensor plays a critical role in the PC240LC-10's Komatsu SAA6D107E-1 engine management system. It directly influences fuel injection timing, idle speed control, and cooling fan operation. When this sensor fails or provides incorrect data, the ECM cannot properly regulate engine temperature, potentially leading to overheating, poor fuel economy, or reduced hydraulic performance.

Common Symptoms

• Engine warning lamp illuminated on the monitor panel with CA2357 displayed
• Cooling fan running continuously at high speed, even during cold starts
• Hard starting or extended cranking time, especially in cold weather conditions
• Rough idle or inconsistent engine RPM during warm-up phase
• Reduced hydraulic response due to ECM entering protective derate mode

Potential Causes

The CA2357 code in used PC240LC-10 excavators typically stems from:

Sensor Degradation: The ECT sensor itself fails internally due to age, with resistance values drifting outside the 200-6,000 ohm specification range. This is extremely common in machines with 5,000+ operating hours.

Wiring Harness Issues: The sensor harness routing near the turbocharger creates a known rub point. Insulation wear exposes wires to grounding against the engine block, causing intermittent short circuits.

Connector Corrosion: The 2-pin Deutsch connector at the sensor accumulates moisture and corrosion, particularly in machines operating in wet or coastal environments.

ECM Internal Fault: Rare but possible—the ECM's analog-to-digital converter circuit may malfunction, especially in machines exposed to electrical surges or improper jump-starting.

How to Troubleshoot and Fix Code CA2357

Step 1: Visual Inspection Power down the machine and inspect the ECT sensor connector (located on the thermostat housing, left side of engine). Check for pushed-out pins, corrosion, or moisture inside the connector. On used excavators, examine the entire harness route from sensor to ECM for abrasion points against metal surfaces.

Step 2: Sensor Resistance Test Disconnect the sensor and measure resistance across its terminals using a digital multimeter. At 68°F (20°C), resistance should read approximately 2,450 ohms. Compare readings against Komatsu's temperature-resistance chart. Replace the sensor (Part# 6754-61-6210) if values deviate more than 10%.

Step 3: Circuit Voltage Check With ignition ON and sensor disconnected, measure voltage at the harness connector. The signal wire (typically green) should show approximately 5.0 volts from the ECM. Ground wire should show continuity to chassis ground with less than 1 ohm resistance.

Step 4: Harness Continuity Test Check for shorts between signal wire and ground throughout the harness length. Pay special attention to the section passing near the exhaust manifold heat shield. For used machines, this is the most common failure point.

Step 5: Clear Code and Monitor After repairs, clear the fault using Komatsu KOMTRAX or aftermarket diagnostic software. Run the engine through a complete heat cycle and monitor for code recurrence.

Disclaimer: This guide provides general diagnostic procedures. Complex electrical issues or ECM programming should be performed by Komatsu-certified technicians with access to proprietary diagnostic equipment and technical service bulletins specific to your machine's serial number.