What is Sumitomo SH240-6 Fault Code 238?

Fault Code 238 on the Sumitomo SH240-6 excavator indicates a malfunction in the engine coolant temperature sensor circuit, specifically detecting an abnormally high voltage signal or open circuit condition. This diagnostic trouble code (DTC) is generated when the Electronic Control Module (ECM) receives voltage readings outside the expected range from the coolant temperature sensor, typically above 4.5 volts when normal operating range should be 0.5-4.0 volts.

This code is critical for the SH240-6 because the engine relies on accurate coolant temperature data to optimize fuel injection timing, manage engine protection systems, and control cooling fan operation. When the ECM cannot trust temperature readings, it defaults to safe-mode parameters that can significantly impact machine performance and fuel efficiency. For used excavators, this sensor circuit is particularly vulnerable to connector corrosion and harness damage from years of exposure to heat cycling and vibration.

Common Symptoms

• Check engine light or malfunction indicator illuminated on the instrument panel
• Engine runs in cold-start enrichment mode continuously, resulting in black smoke and poor fuel economy
• Cooling fan runs constantly at high speed regardless of actual engine temperature
• Difficulty starting when engine is warm, as the ECM cannot properly adjust fuel delivery
• Engine may enter derate mode limiting power output to prevent potential overheating damage

Potential Causes

The most common technical causes for Code 238 on used SH240-6 excavators include:

• Open circuit in the coolant temperature sensor wiring harness, often caused by wire breakage near the engine block mounting point where vibration stress is highest
• Failed coolant temperature sensor with internal circuit degradation (common after 5,000+ operating hours)
• Corroded or loose connector pins at the sensor or ECM side, particularly where moisture intrusion has occurred
• Damaged sensor wiring insulation rubbing against engine components, creating intermittent short-to-voltage conditions
• Faulty ECM internal circuit (rare, but possible in machines with electrical system damage history)

How to Troubleshoot and Fix Code 238

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block (typically near the thermostat housing). Inspect the sensor connector for corrosion, bent pins, or moisture contamination. On used excavators, pay special attention to the wiring harness routing—look for abraded insulation, particularly where wires contact metal surfaces or pass near hot exhaust components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (68°F/20°C), resistance should read approximately 2,000-3,000 ohms. If the reading shows infinite resistance (OL) or zero ohms, replace the sensor. Next, check for continuity in the harness by measuring resistance from the sensor connector to the ECM pins—you should see less than 5 ohms resistance.

Step 3: Voltage Supply Check With the key on and sensor disconnected, measure voltage at the sensor connector harness side. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the signal wire back to the ECM for breaks or shorts. For used machines, remove protective loom covering to inspect for hidden wire damage that's common in older harnesses.

Step 4: Clear Code and Monitor After repairs, use Sumitomo diagnostic software or a compatible scan tool to clear the fault code. Run the engine through a complete heat cycle while monitoring live coolant temperature data to verify the sensor reads progressively from cold (around 2.5 volts) to operating temperature (around 1.5 volts).

---

Disclaimer: This guide provides general troubleshooting information for Sumitomo SH240-6 excavators. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause equipment damage or safety hazards.