Komatsu PC210-10 Fault Code CA351: Complete Diagnostic Guide

What is Komatsu PC210-10 Fault Code CA351?

Fault Code CA351 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the ECM (Engine Control Module) monitoring system. This code triggers when the ECM receives sensor readings outside the manufacturer's specified voltage range of 0.5-4.5V, preventing accurate temperature monitoring of the SAA6D107E-3 engine.

This is a critical fault for the PC210-10 because incorrect coolant temperature data can cause the ECM to miscalculate fuel injection timing, trigger unnecessary engine derates, or fail to protect against genuine overheating conditions. In used excavators, this code often appears due to sensor degradation or harness damage rather than actual engine temperature problems.

Common Symptoms

• Yellow warning light illuminated on the monitor panel with corresponding CA351 error message displayed
• Engine operating in derate mode (reduced power output to 75-80% capacity) as a protective measure
• Inaccurate or erratic temperature gauge readings, often showing constant cold or hot readings regardless of actual engine temperature
• Cooling fan running continuously at high speed, even during cold starts or light-duty operation
• Difficulty starting in cold weather conditions due to improper fuel enrichment calculations

Potential Causes

Coolant temperature sensor failure is the primary cause, particularly in machines with 5,000+ operating hours where sensor element deterioration is common. The sensor's internal thermistor can develop resistance drift or complete failure.

Wiring harness damage at known friction points—specifically where the sensor harness passes near the fuel filter bracket and crosses the engine block mounting tabs—causes intermittent open circuits in used PC210-10 models.

Corroded or loose connector terminals at the sensor plug (3-pin Deutsch connector) allow moisture infiltration, creating voltage signal interference or resistance increases beyond ECM tolerance.

ECM internal fault (less common) where the temperature input circuit board develops cold solder joints or component failure after prolonged exposure to engine bay heat cycles.

How to Troubleshoot and Fix Code CA351

Step 1: Visual Inspection and Connector Check Begin with the engine off and cool. Locate the coolant temperature sensor on the thermostat housing (driver's side of engine block). Disconnect the 3-pin connector and inspect for green corrosion, bent pins, or moisture inside the boot. Clean terminals with electrical contact cleaner and dielectric grease. On used excavators, this simple fix resolves approximately 30% of CA351 codes.

Step 2: Sensor Resistance Testing Using a digital multimeter set to ohms, backprobe the sensor terminals (not the harness). At 68°F (20°C), resistance should read 2,400-2,600 ohms; at 176°F (80°C), expect 300-330 ohms. Values outside this range confirm sensor replacement is required. For used machines, always compare readings against Komatsu's temperature-resistance chart in the service manual.

Step 3: Harness Voltage and Continuity Check With the sensor disconnected and ignition ON (engine off), measure supply voltage at the harness connector—should read 5.0V ±0.2V from the ECM. Check ground circuit continuity to chassis ground (should be less than 1 ohm resistance). Inspect the harness routing for abrasion damage along the block and secure any loose sections with proper standoffs to prevent future chafing.

Step 4: ECM Signal Verification If sensor and wiring test correctly, connect Komatsu KOMTRAX diagnostic software or compatible scan tool to monitor live sensor data while warming the engine. The signal voltage should transition smoothly from 3.5V (cold) to 0.8V (operating temp). Erratic jumps indicate ECM input circuit problems requiring controller diagnostics or replacement.

For used excavators specifically: Always inspect previous repair attempts—look for spliced wires, aftermarket sensors (non-OEM sensors frequently cause repeat failures), and check if connector seals were properly reinstalled. Replace only with genuine Komatsu part number 6261-81-8210 to ensure proper calibration.

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Disclaimer: This guide provides general diagnostic procedures for informational purposes. Always consult the official Komatsu PC210-10 service manual and consider professional diagnosis by certified technicians for complex electrical issues. Improper repairs may cause additional engine management system faults or void remaining warranties on used equipment.