## What is Kobelco SK350LC-8 Fault Code A025?

**Fault Code A025 on the Kobelco SK350LC-8 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM).** This code specifically relates to the electrical circuit that monitors engine operating temperature, which is critical for fuel injection timing, emissions control, and engine protection systems.

The **coolant temperature sensor** (CTS) provides real-time data to the ECM, allowing the machine to adjust performance parameters based on engine temperature. On the SK350LC-8, which typically features Hino J05E or similar tier-compliant diesel engines, proper temperature monitoring prevents overheating, optimizes fuel efficiency, and protects expensive engine components. When this circuit fails or provides erratic readings, the ECM may trigger **power derate modes** or prevent the machine from operating at full capacity to protect the engine from potential thermal damage.

## Common Symptoms

- **Engine warning light** or **check engine light** illuminated on the instrument cluster
- **Reduced engine power** or automatic derate to lower RPM, limiting machine productivity
- **Difficulty starting** when the engine is cold, or prolonged cranking times
- **Cooling fan running continuously** at high speed, even when engine temperature appears normal
- **Black smoke** from exhaust due to improper fuel mixture caused by incorrect temperature data

## Potential Causes

The most common causes of fault code A025 on used Kobelco SK350LC-8 excavators include:

- **Faulty coolant temperature sensor** due to age, corrosion, or internal component degradation
- **Damaged wiring harness** near the engine block where vibration and heat cause wire insulation breakdown (known rub point on SK350LC models)
- **Corroded or loose electrical connectors** at the sensor or ECM, especially common in machines operating in wet or marine environments
- **Low coolant level** exposing the sensor tip and causing false readings
- **Failed ECM** or internal circuit board issues (rare, but occurs in high-hour used machines)
- **Intermittent short circuits** caused by damaged insulation touching grounded metal surfaces

## How to Troubleshoot and Fix Code A025

**Step 1: Visual Inspection and Preliminary Checks**

Begin by checking the **engine coolant level** in the radiator and overflow tank. Low coolant can expose the sensor, triggering false readings. Inspect the **coolant temperature sensor location** (typically near the thermostat housing on the engine block) for physical damage, coolant leaks, or corrosion. On used excavators, pay close attention to **connector condition**—look for green corrosion, moisture intrusion, or damaged pins.

**Step 2: Electrical Circuit Testing**

Using a **digital multimeter**, disconnect the coolant temperature sensor connector 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). If resistance is infinite (open circuit) or near zero (short circuit), the sensor has failed and requires replacement. Additionally, check for **voltage supply** at the harness connector—you should see approximately **5 volts** reference voltage from the ECM.

**Step 3: Wiring Harness Inspection**

Trace the **sensor wiring harness** from the sensor back to the ECM, inspecting for **chafing, cuts, or rub points** where the harness contacts the engine block or frame. The SK350LC-8 is known for harness wear near the engine mount area due to vibration. Check for **continuity** through each wire and verify there are no **shorts to ground**. Replace any damaged sections of harness and secure properly with heat-resistant protective sleeving.

**Step 4: Component Replacement and Verification**

If testing confirms sensor failure, replace with a **genuine Kobelco or OEM-equivalent coolant temperature sensor**. Clean connector terminals with **electrical contact cleaner** and apply **dielectric grease** to prevent future corrosion—critical for used machines. After replacement, clear the fault code using **Kobelco diagnostic software** (KIOS) or a compatible scan tool. Run the engine through a complete warm-up cycle and verify the code does not return.

---

**Disclaimer:** This guide provides general troubleshooting information for Kobelco SK350LC-8 fault code A025. Always consult the official Kobelco service manual for your specific machine serial number and engine configuration. If you're uncomfortable performing electrical diagnostics, contact a certified Kobelco technician or qualified heavy equipment mechanic to prevent incorrect diagnosis or further damage.