Komatsu PC220-8 Fault Code CA155: Complete Diagnostic Guide

What is Komatsu PC220-8 Fault Code CA155?

Fault Code CA155 indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically detecting an abnormally high voltage signal in the sensor's electrical pathway. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) receives a voltage reading outside the acceptable range from the hydraulic oil temperature sensor, typically above 4.8 volts when normal operating range should be 0.5-4.5 volts.

This code is critical for the PC220-8's performance management system. The hydraulic oil temperature sensor provides essential data that the ECM uses to protect hydraulic components, adjust pump output, and prevent overheating damage. When CA155 is active, the machine may enter a protective derate mode, limiting hydraulic performance to prevent potential system damage from operating with inaccurate temperature data.

Common Symptoms

When CA155 is active on your Komatsu PC220-8, you may experience:

• Hydraulic system warning light illuminated on the monitor panel with fault code displayed
• Reduced hydraulic responsiveness or slower cycle times due to protective derate mode
• Inaccurate hydraulic temperature readings showing abnormally high or erratic values on the display
• Intermittent code activation that appears and disappears, especially during machine vibration or operation
• Engine power limitation in severe cases where the ECM restricts performance to protect the hydraulic system

Potential Causes

The most common technical causes for CA155 on used PC220-8 excavators include:

• Open circuit in sensor wiring harness due to wire breakage, particularly at flex points near the hydraulic tank
• Damaged or corroded connector pins at the sensor or ECM connection points (common in machines with 5,000+ hours)
• Failed hydraulic oil temperature sensor with internal circuit breakdown causing high resistance
• Harness chafing against the hydraulic tank mounting bracket—a known wear point on this model
• Moisture intrusion in connectors causing intermittent high-resistance readings
• ECM internal fault (rare, but possible in older machines with electrical system exposure)

How to Troubleshoot and Fix Code CA155

Step 1: Visual Inspection Begin with a thorough inspection of the sensor harness routing from the hydraulic tank to the ECM. On used excavators, carefully check for harness wear where the wiring passes near the tank mounting points and swing bearing area. Inspect the sensor connector for corrosion, bent pins, or oil contamination. Clean connections with electrical contact cleaner and check for physical damage.

Step 2: Sensor Circuit Testing Using a digital multimeter (DMM), perform a resistance check on the hydraulic oil temperature sensor. Disconnect the sensor connector and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms. Compare your reading against Komatsu specifications in the service manual. If resistance is infinite (open circuit) or near zero, the sensor has failed internally.

Step 3: Wiring Harness Continuity and Voltage Check With the sensor disconnected, check harness continuity from the sensor connector back to the ECM. There should be less than 5 ohms resistance on the signal wire. Next, check for voltage supply at the sensor connector with ignition on—you should see approximately 5 volts reference voltage from the ECM. If voltage is present but the circuit tests show high voltage when reconnected, the issue is sensor failure. If there's no reference voltage, trace the harness for breaks or check ECM pin connections.

Step 4: Connector Repair and Verification For used PC220-8 excavators, connector corrosion is extremely common. If you find green corrosion or white oxidation on pins, replace the connector rather than attempting to clean it. Use genuine Komatsu connector repair kits with dielectric grease application. After repairs, clear the code using Komatsu diagnostic software (KDWS) or compatible scan tool and monitor for code recurrence during a 30-minute operating cycle.

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Disclaimer: This guide provides general diagnostic procedures for informational purposes. Hydraulic and electrical system repairs should be performed by qualified technicians with appropriate training and tools. Always consult the official Komatsu PC220-8 service manual and follow proper safety lockout/tagout procedures before performing diagnostics or repairs.