What is Komatsu PC1250-11R Fault Code CA351?

Fault Code CA351 on the Komatsu PC1250-11R indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the water temperature sensor system. This code is generated when the engine control module (ECM) receives sensor data outside the predetermined voltage range, typically between 0.5-4.5 volts for normal operating conditions.

The engine coolant temperature sensor is critical for the PC1250-11R's performance management system. It directly influences fuel injection timing, engine warm-up protocols, and thermal protection strategies. When this sensor circuit fails, the ECM defaults to a pre-programmed temperature value, which can lead to inefficient combustion, increased fuel consumption, and potential engine damage if the machine operates under extreme temperature conditions without accurate monitoring.

Common Symptoms

• Check engine light or warning indicator illuminated on the dashboard with reduced engine power output
• Engine running rich or experiencing hard starts, particularly during cold weather conditions
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Engine derate mode activation, limiting machine to approximately 70-80% of normal power output
• Abnormal exhaust smoke (black smoke) due to improper fuel-to-air ratio adjustments

Potential Causes

The most common technical causes for CA351 on used PC1250-11R excavators include:

• Coolant temperature sensor failure due to internal element degradation (common after 8,000-10,000 operating hours)
• Wiring harness damage at known rub points near the engine block mounting brackets and fuel pump assembly
• Corroded or loose connector pins at the sensor plug, especially on machines operated in coastal or high-humidity environments
• ECM internal circuit failure (rare, but documented on older PC1250 series units)
• Coolant contamination causing sensor probe coating and inaccurate readings
• Ground wire deterioration specific to the engine harness ground cluster near the starter motor

How to Troubleshoot and Fix Code CA351

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located on the engine block's thermostat housing. Check the wiring harness for physical damage, particularly where it routes along the engine valley near hydraulic lines. Examine connector pins for corrosion, bent terminals, or moisture intrusion—a common issue in used excavators.

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 depending on specification. Check voltage supply at the harness connector with ignition on—should read approximately 5 volts reference voltage from the ECM.

Step 3: Circuit Continuity Check Test wire continuity from the sensor connector back to the ECM pins (consult Komatsu service manual for specific pin locations). Resistance should be less than 5 ohms. Check for shorts to ground or power by measuring resistance between signal wire and chassis ground (should read infinite resistance).

Step 4: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX Plus) to monitor real-time sensor data and compare coolant temperature readings with an infrared thermometer measurement. For used excavators, inspect the sensor mounting bore for coolant leaks or thread damage that could affect sensor contact with coolant flow.

Step 5: Repair or Replace If sensor tests fail specifications, replace with genuine Komatsu parts (P/N 7861-93-3320 or equivalent). When replacing, apply appropriate thread sealant and torque to 18-22 ft-lbs. If wiring is damaged, repair using heat-shrink solder connections rather than crimp connectors to ensure long-term reliability in the harsh vibration environment.

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Disclaimer: This guide provides general troubleshooting information for the Komatsu PC1250-11R. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may void warranties or create safety hazards.