What is Sumitomo SH350HD-6 Fault Code 201?

Fault Code 201 on the Sumitomo SH350HD-6 excavator indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor circuit or an abnormal coolant temperature reading. This code is triggered when the Engine Control Module (ECM) detects voltage signals outside the expected range from the ECT sensor, typically indicating either an open circuit, short circuit, or sensor failure.

The ECT sensor plays a critical role in engine management by monitoring coolant temperature and sending real-time data to the ECM. This information controls fuel injection timing, idle speed, and engine protection protocols. On used SH350HD-6 excavators, this code is particularly important because prolonged operation with inaccurate temperature readings can lead to overheating, poor fuel economy, or catastrophic engine damage.

Common Symptoms

When Fault Code 201 is active, operators typically experience:

• Engine warning light illuminated on the instrument cluster with reduced engine performance
• Difficulty starting the engine, especially in cold weather conditions
• Engine running excessively rich or lean, causing black smoke or rough idle
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Engine entering derate mode or limiting power output to prevent potential damage

Potential Causes

Several technical factors can trigger Code 201 on used SH350HD-6 excavators:

• ECT sensor failure due to internal resistance degradation (common after 5,000+ operating hours)
• Damaged or corroded wiring harness connections at the sensor plug or ECM connector
• Wiring harness chafing against the engine block near the thermostat housing (known wear point on this model)
• Coolant contamination causing sensor element coating or corrosion
• ECM internal fault in the temperature monitoring circuit (rare but possible in high-hour machines)
• Incorrect sensor installation or aftermarket sensor incompatibility

How to Troubleshoot and Fix Code 201

Step 1: Visual Inspection Begin by inspecting the ECT sensor located near the thermostat housing on the engine block. Check for coolant leaks, corrosion on the connector pins, and physical damage to the wiring harness. On used excavators, pay special attention to harness routing where it contacts metal surfaces.

Step 2: Electrical Testing Disconnect the ECT sensor connector and use a multimeter to measure resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Check for voltage supply from the ECM (usually 5V reference voltage) at the harness side.

Step 3: Wiring Continuity Check Test continuity between the sensor connector and ECM pins using a wiring diagram. Look for opens, shorts to ground, or high resistance (above 5 ohms). Inspect connectors for bent pins or moisture intrusion—common issues in older machines.

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM-specification ECT sensor and apply dielectric grease to connections. Clear the fault code using diagnostic software (Sumitomo diagnostic tool or compatible interface) and verify repair by monitoring live temperature data.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with excavator systems.