What is Sumitomo SH240-5 Fault Code 336?

Fault Code 336 on the Sumitomo SH240-5 excavator indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the Engine Control Module (ECM). This code is triggered when the ECM receives voltage signals outside the expected range from the coolant temperature sensor, or when the sensor reports temperature values that are physically impossible given operating conditions.

The coolant temperature sensor is a critical component in the SH240-5's engine management system, typically found on the engine block near the thermostat housing. This thermistor-type sensor changes its electrical resistance based on coolant temperature, allowing the ECM to optimize fuel injection timing, idle speed, and engine protection protocols. When this sensor fails or its circuit is compromised, the ECM cannot properly manage engine performance, potentially leading to overheating, poor fuel economy, or unnecessary engine derating.

Common Symptoms

• Check Engine light or warning lamp illuminated on the operator display panel
• Engine running in limp mode with reduced power output or RPM limitation to protect against potential overheating
• Hard starting or rough idle, especially during cold starts when the ECM relies heavily on coolant temperature data
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Inaccurate temperature gauge readings on the instrument cluster, showing either maximum hot or minimum cold readings

Potential Causes

The most common causes of Code 336 on used SH240-5 excavators include:

• Failed coolant temperature sensor due to age-related deterioration or thermal cycling stress (very common on machines with 5,000+ hours)
• Corroded or damaged wiring harness connectors at the sensor plug, often caused by coolant leaks contaminating the electrical connection
• Chafed or broken wires in the harness between the sensor and ECM, particularly at routing points near the engine block where vibration causes wire-to-metal contact
• Contaminated engine coolant causing sensor element fouling or corrosion
• ECM internal circuit failure (rare, but possible on older machines with moisture intrusion history)
• Poor ground connection at the sensor or ECM ground points

How to Troubleshoot and Fix Code 336

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block. Inspect the sensor connector for corrosion, coolant contamination, or pushed-back pins. On used excavators, check for coolant stains indicating leaks near the sensor. Examine the wiring harness for obvious damage, chafing, or repairs from previous owners.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At room temperature (68°F/20°C), resistance should typically read between 2,000-3,000 ohms (consult service manual for exact specifications). Test the harness side by checking for continuity between the sensor signal wire and the ECM connector, and verify the sensor ground circuit shows less than 1 ohm resistance to chassis ground.

Step 3: Live Data Analysis Using Sumitomo diagnostic software or a compatible scan tool, monitor live coolant temperature readings. Compare the sensor reading with actual engine temperature (use an infrared thermometer on the thermostat housing). If readings differ by more than 20°F (10°C), the sensor is likely faulty.

Step 4: Voltage Check With ignition on and sensor disconnected, measure reference voltage at the harness connector (signal wire). You should see approximately 5 volts. If voltage is absent or incorrect, trace the harness for breaks or check ECM power supply circuits.

Step 5: Repair or Replace For used machines, prioritize cleaning corroded connectors with electrical contact cleaner and applying dielectric grease before replacing parts. If the sensor tests faulty, replace it with an OEM or quality aftermarket unit. Always use new O-rings or seals during installation and ensure proper torque specifications to prevent coolant leaks.

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