What is Kobelco SK135SR-2 Fault Code E023?

Fault Code E023 on the Kobelco SK135SR-2 excavator indicates a malfunction in the engine coolant temperature sensor circuit. This code is triggered when the Electronic Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically indicating an open circuit, short circuit, or sensor degradation.

The coolant temperature sensor plays a critical role in engine management by monitoring the temperature of the engine coolant and relaying this data to the ECM. The ECM uses this information to regulate fuel injection timing, idle speed, and emissions controls. On the Kobelco SK135SR-2, which utilizes a precision-tuned Hino diesel engine, accurate temperature readings are essential for optimal combustion efficiency and preventing engine overheating or cold-start issues. When E023 appears, the ECM often defaults to a predetermined temperature value, which can lead to reduced performance and increased fuel consumption.

Common Symptoms

When fault code E023 is active on your SK135SR-2, you may experience:

• Check engine light or malfunction indicator lamp illuminated on the dashboard
• Hard starting, especially during cold weather conditions
• Rough idling or erratic engine RPM fluctuations
• Black smoke from the exhaust due to improper fuel-air mixture
• Reduced engine power or inability to reach operating temperature efficiently

Potential Causes

The most common technical reasons for E023 appearing on used Kobelco SK135SR-2 excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element deterioration (common in machines with 5,000+ operating hours)
• Damaged wiring harness or corroded connector pins at the sensor plug, particularly where the harness routes near the engine block and experiences heat cycling
• Open or short circuit in the signal wire between the sensor and ECM
• Corroded ground connection affecting sensor voltage reference
• ECM internal fault (rare, but possible in older units exposed to moisture intrusion)
• Aftermarket sensor incompatibility if the machine has had previous repairs with non-OEM parts

How to Troubleshoot and Fix Code E023

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the wiring harness for physical damage, chafing against metal surfaces, or heat degradation. On used SK135SR-2 models, check for corrosion on the connector terminals and ensure the locking tab is secure. Clean any corrosion with electrical contact cleaner.

Step 2: Sensor Resistance Test Disconnect the sensor and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (approximately 20°C/68°F), resistance should typically read between 2,000-3,000 ohms. Compare your reading with Kobelco specifications. If resistance is infinite (open circuit) or near zero (short circuit), replace the sensor with an OEM Kobelco part.

Step 3: Circuit Voltage Check With the 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, trace the signal wire back to the ECM for breaks or shorts to ground. Pay special attention to areas where the harness may rub against the engine frame—a common failure point on used machines.

Step 4: Ground Circuit Verification Verify continuity between the sensor ground terminal and chassis ground. Resistance should be less than 1 ohm. Clean and retighten ground connections if necessary, as corrosion from coolant leaks is common on older excavators.

Step 5: Clear Code and Test After repairs, use Kobelco-compatible diagnostic software or a generic OBD scanner to clear the fault code. Run the engine through warm-up cycles and monitor for code recurrence. For used excavators, replacing the sensor preventatively during major services can avoid future downtime.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Kobelco service manual for your specific serial number and seek professional assistance from a certified technician for complex electrical diagnostics or if you're unfamiliar with high-voltage systems.