What is Kobelco SK140LC-8 Fault Code 20122?

Fault Code 20122 on the Kobelco SK140LC-8 indicates a malfunction in the engine coolant temperature sensor circuit, specifically an abnormal voltage signal or open circuit condition detected by the Engine Control Module (ECM). This code triggers when the ECM receives voltage readings outside the acceptable range from the coolant temperature sensor, preventing accurate engine temperature monitoring.

The coolant temperature sensor plays a critical role in the SK140LC-8's performance management. It feeds real-time data to the ECM, which adjusts fuel injection timing, idle speed, and activates cooling fan cycles. When this sensor circuit fails, the engine may operate inefficiently, run too rich or lean, and potentially overheat without proper warning—making this a priority repair for maintaining machine longevity and preventing catastrophic engine damage.

Common Symptoms

When Code 20122 is active on your Kobelco SK140LC-8, operators typically experience:

• Check Engine Light illuminated on the instrument panel with reduced engine power
• Engine runs at higher-than-normal idle speeds or fails to reach normal operating temperature
• Cooling fan runs continuously, even when engine is cold
• White or black smoke from exhaust due to incorrect fuel mixture compensation
• Difficult cold starts or extended warm-up periods before normal operation

Potential Causes

The most common technical causes for Code 20122 on used SK140LC-8 excavators include:

• Faulty coolant temperature sensor due to internal resistance degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug, especially where harness contacts engine block
• Open circuit in wiring between sensor and ECM caused by vibration-induced wire breakage
• Corroded or loose ground connections affecting sensor circuit integrity
• Contaminated coolant causing sensor element fouling or scaling
• ECM internal fault (rare, but possible on older machines with 8,000+ hours)

How to Troubleshoot and Fix Code 20122

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block near the thermostat housing. Inspect the sensor connector for corrosion, moisture intrusion, or damaged pins—common issues on used excavators exposed to harsh jobsite conditions. Check the wiring harness for visible damage, particularly at points where it contacts metal surfaces or routing clips.

Step 2: Electrical Testing Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should typically read 2,000-3,000 ohms (consult Kobelco service manual for exact specifications). Test the harness for continuity from sensor connector to ECM pins, checking for open circuits or shorts to ground.

Step 3: Live Voltage Check With ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace wiring for breaks or check ECM connector integrity.

Step 4: Component Replacement If testing confirms sensor failure, replace with genuine Kobelco or OEM-equivalent parts. On used excavators, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear fault codes using diagnostic software like Kobelco SICS (Shop Information & Communication System) and perform a test run to verify repair.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific serial number and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with high-voltage systems.