What is Kobelco SK135SR-2 Fault Code G043?

Fault Code G043 on the Kobelco SK135SR-2 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code specifically relates to the engine's thermal management system, which monitors coolant temperature to optimize engine performance, prevent overheating, and regulate fuel injection timing.

The coolant temperature sensor (CTS) is a critical thermistor-type component that sends voltage signals to the ECM based on coolant temperature variations. When the sensor circuit experiences voltage irregularities, open circuits, short circuits, or reads temperatures outside the normal operating range (typically -40°C to 140°C), the system triggers Code G043. For the SK135SR-2's diesel engine, proper coolant temperature monitoring is essential for maintaining optimal combustion efficiency, preventing thermal damage, and ensuring the machine operates within Tier 2/Tier 3 emissions standards.

Common Symptoms

When Code G043 is active on your Kobelco SK135SR-2, you may experience:

• Check Engine Light or warning lamp illuminated on the instrument cluster
• Hard starting conditions, especially during cold starts when the ECM cannot properly enrich the fuel mixture
• Rough idling or irregular engine RPM fluctuations due to improper fuel compensation
• Engine cooling fan running continuously at maximum speed, regardless of actual operating temperature
• Reduced engine performance or power output as the ECM enters a protective derate mode to prevent potential overheating damage

Potential Causes

The most common technical reasons for Code G043 appearing on used SK135SR-2 excavators include:

• Faulty coolant temperature sensor – sensor element degradation is common after 5,000+ operating hours
• Damaged sensor wiring harness – particularly at the routing point near the engine block where vibration and heat cause insulation breakdown
• Corroded or loose electrical connectors – moisture intrusion at the 2-pin sensor connector is frequent on older machines
• Low coolant level or air pockets in the cooling system causing inaccurate temperature readings
• ECM internal fault – rare but possible on machines with 8,000+ hours or electrical system exposure to moisture
• Ground circuit failure between the sensor and ECM, common where chassis ground points corrode

How to Troubleshoot and Fix Code G043

Step 1: Visual Inspection and Coolant Level Check Begin by inspecting the coolant reservoir and radiator levels. Low coolant creates air pockets around the sensor, causing false readings. Check the sensor wiring harness from the coolant temperature sensor (located near the thermostat housing) to the ECM for visible damage, abrasion, or heat deterioration. On used excavators, pay special attention to areas where the harness contacts the engine block or frame – these are common rub points.

Step 2: Electrical Testing with Multimeter Disconnect the 2-pin connector at the coolant temperature sensor. Using a digital multimeter, measure resistance across the sensor terminals at ambient temperature – you should see approximately 2,000-3,000 ohms at 20°C (resistance decreases as temperature increases). Compare readings to Kobelco's specification chart. Next, check for continuity between the sensor ground wire and chassis ground. Also measure reference voltage from the ECM side of the connector – you should see approximately 5 volts on the signal wire with ignition on.

Step 3: Component Replacement and System Reset If resistance values are out of specification or the sensor shows open/short circuit conditions, replace the coolant temperature sensor with a genuine Kobelco or OEM-equivalent part. Before installation, clean the sensor mounting bore and apply appropriate thread sealant. After replacement, inspect all connector pins for corrosion and apply dielectric grease. Clear the fault code using Kobelco diagnostic software or a compatible J1939 scan tool. Monitor coolant temperature readings during warm-up to verify proper sensor operation (gradual increase from ambient to approximately 82-95°C operating temperature).

For used excavators with persistent codes after sensor replacement, inspect the ECM harness connector for "terminal push-back" – a common issue where connector pins loosen from vibration over time, causing intermittent signal loss.

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Disclaimer: This guide provides general troubleshooting information for Code G043. Always consult the Kobelco SK135SR-2 service manual for model-specific procedures and specifications. If you're uncomfortable performing electrical diagnostics, contact a certified Kobelco technician or qualified heavy equipment mechanic to prevent further damage to electrical systems.