Sumitomo SH700LHD-5B Fault Code 2138: Meaning and Troubleshooting Guide

What is Sumitomo SH700LHD-5B Fault Code 2138?

Fault Code 2138 on the Sumitomo SH700LHD-5B indicates a malfunction in the Fuel Temperature Sensor Circuit, specifically detecting an abnormally high voltage signal being sent to the Engine Control Module (ECM). This code is triggered when the ECM receives a voltage reading from the fuel temperature sensor that exceeds the manufacturer's specified threshold, typically above 4.8-5.0 volts.

The fuel temperature sensor plays a critical role in engine performance by monitoring diesel fuel temperature and allowing the ECM to adjust fuel injection timing and volume accordingly. On high-hour used excavators like the SH700LHD-5B, this sensor helps prevent fuel system damage from overheating and maintains optimal combustion efficiency. When this circuit fails, the engine may enter a protective derate mode or experience reduced power output to prevent potential damage.

Common Symptoms

When Code 2138 is active on your Sumitomo excavator, you may experience:

• Check Engine Light or malfunction warning lamp illuminated on the operator display panel
• Noticeable power loss or engine performance reduction, particularly under heavy loads
• Engine running rougher than normal due to improper fuel delivery adjustments
• Hard starting conditions, especially in cold weather when fuel temperature compensation is critical
• Stored fault code in the ECM memory even after the immediate issue appears resolved

Potential Causes

The most common technical reasons for Code 2138 on used SH700LHD-5B excavators include:

• Open circuit in the fuel temperature sensor wiring harness, often caused by wire breakage near flex points around the fuel tank or engine mount areas
• Failed fuel temperature sensor with internal short circuit, common on machines with 8,000+ operating hours
• Corroded or damaged connector pins at the sensor or ECM connection points due to moisture infiltration
• Harness chafing against frame components or fuel lines, particularly where the harness routes along the chassis rail
• Faulty ECM (rare, but possible on older machines with electrical system damage from previous issues)

How to Troubleshoot and Fix Code 2138

Step 1: Visual Inspection Begin by inspecting the fuel temperature sensor located on the fuel filter housing or fuel rail (consult your service manual for exact location). Check the wiring harness from sensor to ECM for visible damage, abrasion points, or melted insulation. On used excavators, pay special attention to areas where the harness passes near hot components or moving parts.

Step 2: Connector and Pin Examination Disconnect the fuel temperature sensor connector and thoroughly inspect both male and female pins for corrosion, bent terminals, or moisture. Clean contacts with electrical contact cleaner and check for proper pin tension. This is a critical step on high-hour machines where environmental contamination is common.

Step 3: Sensor Resistance Testing Using a digital multimeter, measure the resistance across the fuel temperature sensor terminals. At 68°F (20°C), resistance should typically read between 2,000-3,000 ohms (verify exact specification in your service manual). If the reading shows infinite resistance (open circuit) or near-zero ohms (short circuit), replace the sensor.

Step 4: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the ECM side of the harness connector. You should see approximately 5 volts reference voltage from the ECM. If voltage is absent or incorrect, trace the wiring for breaks or shorts to ground.

Step 5: Harness Continuity Test Test continuity between the sensor connector and ECM pins (refer to wiring diagrams for specific pin numbers). Any reading above 5 ohms indicates excessive resistance from corroded connections or damaged wiring requiring repair or replacement.

Step 6: Clear Code and Verify After repairs, clear the fault code using Sumitomo diagnostic software or a compatible scan tool. Operate the machine under normal working conditions and monitor for code recurrence.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Sumitomo service manual for your specific machine serial number. If you're unfamiliar with electrical diagnostics or lack proper tools, consult a certified Sumitomo dealer or qualified heavy equipment technician to avoid causing additional damage to the electrical system.