What is Komatsu PC200-8 Fault Code CA155?

Komatsu PC200-8 fault code CA155 indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically detecting an abnormal voltage signal or open/short circuit condition in the sensor wiring. This Diagnostic Trouble Code (DTC) is generated by the machine's Electronic Control Module (ECM) when it receives voltage readings outside the expected range from the hydraulic oil temperature sensor located in the hydraulic tank.

This code is critical for the PC200-8's performance because the ECM relies on accurate hydraulic oil temperature data to optimize pump flow, protect system components from overheating, and prevent premature wear. When CA155 triggers, the system may default to conservative operating parameters, reducing machine efficiency and potentially causing unnecessary component stress.

Common Symptoms

When fault code CA155 is active on your Komatsu PC200-8, you may experience:

• Monitor panel warning light illuminated, often accompanied by a specific hydraulic system alert message
• Reduced hydraulic response or slower cycle times as the ECM enters a protective derate mode
• Inaccurate temperature readings displayed on the monitor, showing extremely high, low, or erratic values
• Intermittent alarm activation that may clear and return, especially during machine warm-up or under varying loads
• Machine performance limitations during cold starts, as the ECM cannot properly manage warm-up sequences

Potential Causes

The most common technical causes for CA155 on used PC200-8 excavators include:

• Damaged or corroded sensor connector at the hydraulic tank mounting point, frequently exposed to moisture and debris
• Broken or frayed wiring harness along known wear points near the swing bearing or tank mounting brackets
• Failed hydraulic oil temperature sensor, particularly in machines with 6,000+ operating hours where sensor drift occurs
• ECM internal fault or corrupted calibration data (less common but possible in older units)
• Poor ground connection at the sensor or ECM grounding points, causing voltage reference issues
• Aftermarket hydraulic oil incompatibility affecting sensor element resistance characteristics

How to Troubleshoot and Fix Code CA155

Step 1: Visual Inspection and Connector Check Begin by locating the hydraulic oil temperature sensor on the left side of the hydraulic tank. Disconnect the sensor connector and inspect for corrosion, bent pins, or moisture intrusion. On used excavators, this connector often accumulates hydraulic mist and dirt. Clean thoroughly with electrical contact cleaner and check for physical damage.

Step 2: Sensor Resistance Testing Using a digital multimeter, measure the sensor's resistance. At approximately 20°C (68°F), the sensor should read between 2,000-3,000 ohms (consult your service manual for exact specifications). Test resistance while gently heating the sensor tip with a heat gun—resistance should decrease smoothly as temperature increases. Erratic readings indicate sensor failure.

Step 3: Wiring Harness Continuity and Voltage Check Trace the sensor harness from the tank to the ECM, paying special attention to routing near the swing motor and frame rails where abrasion commonly occurs on used machines. Check for continuity between sensor pins and ECM connector terminals. With the ignition on and sensor disconnected, verify 5-volt reference voltage at the harness connector using your multimeter.

Step 4: Ground Circuit Verification Verify the ground circuit integrity by measuring resistance between the sensor ground pin and chassis ground—it should read less than 1 ohm. Corroded ground connections are particularly common in machines operating in coastal or high-humidity environments.

Step 5: Component Replacement and System Reset If testing confirms sensor failure, replace with a genuine Komatsu part (part number 7861-93-3320 or equivalent). After replacement, clear the fault code using Komatsu diagnostic software (KTEC) or a compatible scan tool, and perform a complete system test cycle to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC200-8 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause further damage or safety hazards.