What is Sumitomo SH240-5 Fault Code 202?

Fault Code 202 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 Electronic Control Module (ECM). This code specifically relates to the coolant temperature sensor sending irregular voltage signals to the ECM, preventing accurate monitoring of engine operating temperatures.

The coolant temperature sensor is critical for the SH240-5's engine management system, as it directly influences fuel injection timing, idle speed control, and engine protection protocols. When this sensor circuit fails, the ECM cannot properly regulate engine performance, potentially leading to overheating, poor fuel economy, or engine damage. For used excavators, this fault often stems from sensor degradation, corroded connectors, or wiring harness damage accumulated over years of operation in harsh construction environments.

Common Symptoms

• Check Engine Light or warning lamp illuminated on the instrument panel
• Engine running in limp mode with reduced power output and limited RPM range
• Difficulty starting the engine, especially during cold weather conditions
• Erratic engine idle or irregular RPM fluctuations during warm-up
• Engine cooling fan running continuously at full speed regardless of actual temperature

Potential Causes

The most common technical causes for Code 202 on used SH240-5 excavators include:

• Coolant temperature sensor failure due to internal resistance drift or element corrosion
• Damaged or frayed wiring harness between the sensor and ECM, particularly at flex points near the engine block
• Corroded or loose electrical connectors at the sensor or ECM terminals
• Low coolant level causing sensor exposure to air, resulting in false readings
• ECM internal fault affecting the sensor input circuit (less common but possible in high-hour machines)
• Contaminated coolant causing sensor probe fouling or mineral deposits

How to Troubleshoot and Fix Code 202

Step 1: Visual Inspection Begin by checking coolant level and condition. Inspect the coolant temperature sensor (typically located on the engine block or thermostat housing) for physical damage, coolant leaks, or corrosion. On used excavators, carefully examine the entire wiring harness from sensor to ECM for wear, particularly where the harness contacts metal surfaces or passes through grommets.

Step 2: Electrical Testing Disconnect the coolant temperature sensor connector. Using a digital multimeter, measure the sensor's resistance at various temperatures (consult Sumitomo specifications—typically 2,000-3,000 ohms at 68°F). Check for voltage supply at the harness connector (usually 5V reference from ECM). Inspect connector pins for corrosion, bent terminals, or moisture intrusion—common issues in older machines.

Step 3: Circuit Verification Test harness continuity between the sensor connector and ECM using a wiring diagram. Check for short circuits to ground or other wires. For used excavators, pay special attention to harness sections near heat sources or moving components where insulation may have deteriorated over time.

Step 4: Component Replacement If testing confirms sensor failure, replace with an OEM or quality aftermarket coolant temperature sensor. Clean connector terminals with electrical contact cleaner and apply dielectric grease. Clear codes using Sumitomo diagnostic software or compatible scan tool and verify repair through a test cycle.

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Disclaimer: This guide provides general troubleshooting information. Always consult the Sumitomo SH240-5 service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper tools and training.