What is Komatsu PC210LC-8 Fault Code CA731?

Fault Code CA731 indicates a malfunction in the hydraulic oil temperature sensor circuit within the Komatsu PC210LC-8's control system. This diagnostic trouble code (DTC) is triggered when the machine's Electronic Control Module (ECM) detects an abnormal voltage signal from the hydraulic oil temperature sensor, typically due to an open circuit, short circuit, or sensor failure.

The hydraulic oil temperature sensor plays a critical role in protecting the PC210LC-8's hydraulic system by monitoring operating temperatures and preventing overheating damage. When this sensor malfunctions, the ECM cannot accurately assess hydraulic oil conditions, potentially leading to reduced machine performance, derated power output, or automatic shutdown protocols to prevent catastrophic hydraulic system damage. For used excavators, this code often signals age-related sensor degradation or wiring harness issues common in machines with 5,000+ operating hours.

Common Symptoms

• Warning lamp illumination on the instrument cluster, often accompanied by a hydraulic temperature warning icon
• Reduced hydraulic response or sluggish boom/arm/bucket movements as the ECM enters protective mode
• Intermittent error codes that appear and disappear, especially during cold starts or under heavy load conditions
• Engine power derate or automatic throttle reduction when the system assumes overheating conditions
• Error message display on the monitor panel reading "Hydraulic Oil Temp Sensor Error" or similar warning text

Potential Causes

The most common technical failures triggering CA731 on used PC210LC-8 excavators include:

• Sensor element failure due to thermal cycling fatigue or internal resistor degradation (common after 6,000-8,000 hours)
• Wiring harness damage at known rub points near the hydraulic tank mounting bracket or along the right-side chassis rail
• Connector corrosion at the sensor plug connection, particularly on machines operated in coastal or high-moisture environments
• Broken or frayed wires in the sensor circuit between the sensor and main wiring harness connector behind the operator's cab
• ECM internal circuit failure (rare, but documented in early production PC210LC-8 models from 2008-2010)
• Poor ground connections at chassis grounding points G3 or G5 specific to the hydraulic monitoring circuit

How to Troubleshoot and Fix Code CA731

Step 1: Visual Inspection and Connector Check Begin by locating the hydraulic oil temperature sensor mounted on the hydraulic oil tank (typically on the left side near the return filter). Disconnect the two-pin connector and inspect for corrosion, bent pins, or moisture intrusion. On used excavators, pay special attention to the rubber connector seal—deterioration here allows moisture to create intermittent faults. Clean contacts with electrical contact cleaner and apply dielectric grease before reconnection.

Step 2: Sensor Resistance Testing Using a digital multimeter (DMM), measure resistance across the sensor terminals with the sensor disconnected. At 20°C (68°F), resistance should read approximately 2,200-2,800 ohms (verify exact specifications in Komatsu service manual SSM-3). If readings are infinite (open circuit) or near zero (short circuit), replace the sensor with genuine Komatsu part number 7861-93-3320 or verified equivalent.

Step 3: Wiring Harness Continuity Test Trace the sensor circuit wiring from the sensor connector to the main harness connector X2 behind the cab. Check for continuity between sensor pins and corresponding ECM pins (typically B17 and B18). On used machines, physically inspect the harness routing near the hydraulic tank bracket—this is a known wear point where vibration causes wire insulation breakdown. Repair any damaged sections with heat-shrink solder connections rather than crimp connectors for lasting durability.

Step 4: Voltage Supply Verification With ignition on (engine off), measure 5-volt reference voltage from the ECM at the sensor connector. Low or absent voltage indicates ECM circuit issues or blown fuses in the monitoring system power supply. Check Fuse F-7 (10A) in the main fuse box under the operator's seat.

Step 5: Clear Code and Monitor After repairs, clear the fault code using Komatsu KOMTRAX diagnostic software or compatible diagnostic tool. Run the machine through a complete warm-up cycle while monitoring live hydraulic temperature data to confirm proper sensor operation and stable voltage signals.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu service manual for your specific machine serial number, and consider professional diagnostic services for complex electrical issues. Improper repairs may void warranties or create safety hazards.