What is Komatsu PC1250-11R Fault Code CA325?

Fault Code CA325 indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormal voltage signal or open circuit condition in the sensor system. This code is triggered when the Electronic Control Module (ECM) receives voltage readings outside the expected range (typically 0.2-4.8V) from the coolant temperature sensor located on the engine block.

For the Komatsu PC1250-11R, this diagnostic trouble code is critical because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, govern engine protection protocols, and manage hydraulic system performance. When this sensor circuit fails, the engine may enter a derate mode to prevent potential overheating damage, significantly impacting machine productivity on job sites.

Common Symptoms

• Engine warning lamp illuminated on the monitor panel with reduced engine power output
• Engine derate mode activated, limiting maximum RPM to approximately 1,400-1,600 RPM
• Difficulty starting in cold weather conditions due to improper fuel enrichment
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Inaccurate temperature readings displayed on the operator monitor (often showing extremely high or low values)

Potential Causes

The most frequent causes of CA325 on used PC1250-11R excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Wiring harness damage at known rub points near the engine mount brackets and fuel injection pump
• Corroded or loose connector pins at the sensor plug, especially on machines operating in high-moisture environments
• ECM internal circuit failure (less common but possible on high-hour machines)
• Damaged sensor threads causing poor thermal contact with engine block, affecting signal accuracy
• Aftermarket sensor incompatibility if previous repairs used non-OEM components

How to Troubleshoot and Fix Code CA325

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor and its wiring harness for obvious damage. On used excavators, check for harness chafing against the engine block, melted insulation near hot exhaust components, and corrosion at the connector. Disconnect the sensor and examine both male and female connector pins for green corrosion or bent terminals.

Step 2: Electrical Testing Using a digital multimeter, measure sensor resistance with the engine cold (should read approximately 2,000-3,000 ohms at 20°C). Check harness continuity from the sensor connector back to the ECM (pin locations specified in service manual). Measure supply voltage at the sensor connector with ignition on—should read approximately 5 volts. Any reading below 4.5V or above 5.5V indicates a harness or ECM power supply issue.

Step 3: Component Replacement and Verification If resistance and voltage tests fail, replace the coolant temperature sensor using genuine Komatsu parts (part number 6261-81-6310 or equivalent). For used machines with high hours, inspect the sensor mounting boss for thread damage or coolant contamination. After installation, clear fault codes using Komatsu diagnostic software (KOMTRAX) and perform a road test, monitoring live data to confirm temperature readings correlate with actual engine warmth.

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