What is Komatsu PC210-8 Fault Code CA155?

Komatsu PC210-8 fault code CA155 indicates a malfunction in the Boom Priority Solenoid Valve circuit, specifically detecting an open circuit or abnormal voltage condition within the hydraulic control system. This code is generated by the machine's Electronic Control Module (ECM) when it cannot properly energize or communicate with the boom priority valve, which regulates hydraulic flow prioritization during simultaneous multi-function operations.

The boom priority solenoid is critical for optimizing hydraulic performance on the PC210-8, ensuring that boom functions receive adequate flow even when multiple circuits are activated simultaneously. When this system fails, operators experience reduced productivity and potential hydraulic conflicts that can accelerate component wear. This fault is particularly common in used excavators due to harness degradation and connector corrosion from jobsite environmental exposure.

Common Symptoms

• Boom Priority Warning Lamp illuminated on the monitor panel, often accompanied by audible alarm
• Sluggish or weak boom response, especially when operating boom and arm functions simultaneously
• Loss of hydraulic flow prioritization, causing noticeably slower cycle times during combined operations
• Intermittent loss of boom function that may restore temporarily after key cycle
• Machine may enter derated mode, limiting engine RPM to protect hydraulic components

Potential Causes

The most frequent causes of CA155 on used PC210-8 excavators include:

• Open circuit in the wiring harness between the ECM and boom priority solenoid valve, often from harness rubbing near the boom foot pin area
• Failed boom priority solenoid valve coil, typically showing infinite resistance instead of the specified 10-15 ohms
• Corroded or damaged connector pins at the X2 harness connector located behind the cab
• ECM internal driver circuit failure, though less common than external wiring issues
• Water intrusion into the solenoid valve connector, common on machines operated in wet conditions
• Broken or chafed wiring at known rub points where the harness contacts the frame near the hydraulic tank

How to Troubleshoot and Fix Code CA155

Step 1: Visual Inspection Begin with a thorough inspection of the wiring harness routing from the ECM to the boom priority solenoid valve located on the main control valve. Check for obvious damage, particularly where the harness passes near the swing bearing and boom cylinder area. Inspect the X2 connector for corrosion, bent pins, or moisture contamination—a common issue on used equipment.

Step 2: Resistance Testing Disconnect the solenoid valve connector and use a digital multimeter to measure resistance across the solenoid coil terminals. You should read approximately 10-15 ohms at 20°C. An infinite reading confirms coil failure. Next, check continuity from the connector back to the ECM pins with the harness disconnected—any reading above 2 ohms indicates excessive resistance from corrosion or breaks.

Step 3: Voltage Supply Verification With the key on and engine off, backprobe the solenoid connector to verify battery voltage (24V) on the supply wire. If voltage is absent, trace back toward the ECM and check the main relay and associated fuses. For used excavators, pay special attention to ground connections, as corrosion at grounding points near the hydraulic tank frequently causes erratic voltage readings.

Step 4: Component Replacement and Verification If diagnostics confirm solenoid failure, replace the boom priority solenoid valve using genuine Komatsu parts (Part #: 702-21-57500). After replacement, clear the code using Komatsu diagnostic software (KOMTRAX) or an aftermarket tool, then perform functional testing under load. For harness damage, repair using proper gauge wire and seal connectors with dielectric grease to prevent future moisture ingress.

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Disclaimer: This guide provides general diagnostic procedures for informational purposes. Hydraulic system repairs involve pressurized components and electrical systems. Always consult the Komatsu PC210-8 service manual and consider professional technician assistance for complex diagnostics or if you lack proper training and equipment.