What is Komatsu PC138US-8 Fault Code CA145?

Fault Code CA145 indicates a malfunction in the hydraulic oil temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition in the sensor system. This code is generated when the machine's controller (ECM) receives a voltage reading outside the normal operational range from the hydraulic oil temperature sensor, typically above 4.5 volts when the expected range is 0.5-4.5 volts.

For the Komatsu PC138US-8, this sensor plays a critical role in protecting the hydraulic system by monitoring oil temperature and triggering derate modes or shutdown protocols when temperatures exceed safe operating limits. When CA145 is active, the ECM loses accurate temperature data, potentially allowing the machine to operate with overheated hydraulic oil, risking component damage to pumps, motors, and seals.

Common Symptoms

• Warning lamp illuminated on the monitor panel with fault code CA145 displayed
• Hydraulic system performance issues, including sluggish operation or reduced power, especially when the machine enters protective derate mode
• Inaccurate temperature readings on the display, often showing extremely high or no temperature reading at all
• Intermittent fault activation that may appear and disappear, particularly during machine warm-up or when operating in varying ambient temperatures
• Automatic engine derate or shutdown if the ECM cannot verify safe hydraulic oil temperature

Potential Causes

The most common causes of CA145 on used PC138US-8 excavators include:

• Failed hydraulic oil temperature sensor due to internal sensor element degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector points near the hydraulic tank where vibration and heat exposure are highest
• Open circuit condition caused by broken wires, often found where the harness routes along the swing bearing or upper structure
• Corroded connector pins at the sensor connection point due to moisture intrusion in the engine compartment
• ECM internal circuit failure (less common, but possible in machines with electrical system damage history)
• Poor ground connection at the sensor mounting location due to rust or paint buildup on older machines

How to Troubleshoot and Fix Code CA145

Step 1: Visual Inspection Begin by locating the hydraulic oil temperature sensor on the hydraulic tank (typically mounted on the side or bottom of the reservoir). Inspect the sensor connector for corrosion, oil contamination, or damaged pins. On used excavators, check for harness wear where wiring contacts metal edges or routing brackets. Clean connectors with electrical contact cleaner and ensure positive connection.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult your service manual for exact specifications). Next, check for continuity in the wiring harness from the sensor connector to the ECM connector. Measure voltage at the sensor connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Sensor and Harness Replacement If resistance readings are out of specification or the sensor shows infinite resistance (open circuit), replace the hydraulic oil temperature sensor with a genuine Komatsu part (part number specific to PC138US-8). If wiring shows breaks or high resistance (above 5 ohms), repair or replace the affected harness section. For used machines, apply dielectric grease to all reconnected terminals to prevent future corrosion. After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool and verify the code does not return during a 30-minute operational test.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC138US-8 service manual and consider professional diagnosis, especially for complex electrical issues or if you're unfamiliar with high-voltage systems. Improper repairs may void warranties or create safety hazards.