Sumitomo SH220LC-5 Fault Code 1093: Complete Diagnostic Guide

What is Sumitomo SH220LC-5 Fault Code 1093?

Fault Code 1093 on the Sumitomo SH220LC-5 indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the ECM (Engine Control Module). This code typically signals that the ECM has detected either an open circuit, short circuit, or implausible voltage signal from the coolant temperature sensor.

The coolant temperature sensor plays a critical role in the SH220LC-5's performance by providing real-time data to the ECM for fuel injection timing, engine warm-up cycles, and protection against overheating. When this sensor circuit fails, the engine may default to "limp mode" or use predetermined temperature values, significantly affecting fuel efficiency, hydraulic response, and overall machine productivity. For used excavators, this sensor and its wiring harness are particularly vulnerable to heat cycling damage and corrosion.

Common Symptoms

When Code 1093 is active on your SH220LC-5, operators typically experience:

• Engine warning light illuminated on the dashboard or check engine lamp flashing
• Hard starting or rough idle, especially during cold starts when the ECM cannot properly adjust fuel mixture
• Engine derate or power reduction as the ECM enters protective mode
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Increased fuel consumption due to improper fuel-air mixture calculations
• Black or white smoke from exhaust during operation

Potential Causes

The most common technical reasons for Code 1093 on used SH220LC-5 excavators include:

• Faulty coolant temperature sensor – Internal sensor element failure due to age or thermal stress
• Damaged wiring harness – Wire insulation breakdown near engine block where heat and vibration cause friction wear
• Corroded or loose connector pins – Moisture intrusion at the sensor connector, common in machines operating in wet conditions
• ECM internal fault – Less common, but possible in high-hour machines with electrical system degradation
• Poor ground connection – Corroded ground strap or mounting bolt causing intermittent signal loss
• Coolant contamination affecting sensor – Debris or oil in coolant coating sensor element

How to Troubleshoot and Fix Code 1093

Step 1: Visual Inspection Begin by locating the coolant temperature sensor (typically mounted on the engine block near the thermostat housing). Inspect the wiring harness from sensor to ECM for visible damage, chafing against brackets, or melted insulation. On used excavators, pay special attention to harness routing near moving engine components and exhaust manifolds where heat damage is common.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals. At room temperature (20°C/68°F), resistance should typically read 2,000-3,000 ohms (consult your service manual for exact specifications). Also check for voltage supply at the harness connector—you should see approximately 5 volts reference voltage from the ECM with key on, engine off.

Step 3: Circuit Continuity Check Test harness continuity from the sensor connector back to the ECM pins using a wiring diagram. Check for shorts to ground or power by measuring resistance between each wire and chassis ground (should read infinite resistance). Inspect connector pins for corrosion or bent terminals, cleaning with electrical contact cleaner if necessary.

Step 4: Sensor Replacement and Verification If testing confirms sensor failure, replace with an OEM or quality aftermarket coolant temperature sensor. Apply dielectric grease to connector terminals before reconnection. Clear the fault code using diagnostic software (Sumitomo diagnostic tool or compatible scan tool), then monitor during a full warm-up cycle to verify proper operation.

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Disclaimer: This guide provides general diagnostic procedures for Code 1093. Always consult the Sumitomo SH220LC-5 service manual for model-specific specifications. If you're uncomfortable performing electrical diagnostics, consult a certified heavy equipment technician to avoid further damage to the electrical system.