What is Sumitomo SH220LC-6 Fault Code 112?

Fault Code 112 on the Sumitomo SH220LC-6 excavator indicates an Engine Speed Sensor (RPM Sensor) circuit malfunction or signal error. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal or missing signal from the engine speed sensor, which monitors crankshaft rotation and provides critical data for fuel injection timing, governor control, and overall engine management.

This code is particularly critical for the SH220LC-6 because the engine speed sensor directly influences the machine's ability to maintain proper idle speed, respond to throttle inputs, and coordinate hydraulic pump output with engine RPM. Without accurate RPM data, the ECM cannot optimize fuel delivery, potentially causing poor performance, increased fuel consumption, or complete engine shutdown in severe cases.

Common Symptoms

When Fault Code 112 is active on your Sumitomo SH220LC-6, you may experience:

• Engine fails to start or cranks but won't fire due to lack of RPM signal to the ECM
• Erratic idle speed with hunting or stalling, especially when hydraulics are engaged
• Loss of engine power or inability to reach full RPM under load
• Check engine light or warning lamp illuminated on the instrument cluster
• Intermittent engine shutdown during operation, particularly when machine vibration increases

Potential Causes

The most common technical causes for Code 112 on used SH220LC-6 excavators include:

• Failed or contaminated engine speed sensor (magnetic pickup sensor) due to age, heat exposure, or metallic debris buildup on the sensor tip
• Damaged or corroded wiring harness between the sensor and ECM, especially at connector pins prone to moisture intrusion
• Broken or loose sensor mounting, causing improper air gap between sensor and flywheel/crankshaft gear teeth
• Worn flywheel ring gear with missing or damaged teeth preventing consistent signal generation
• ECM internal fault or corrupted software (less common but possible in high-hour machines)
• Poor ground connections at engine block or chassis ground points affecting sensor circuit integrity

How to Troubleshoot and Fix Code 112

Step 1: Visual Inspection Begin by locating the engine speed sensor (typically mounted on the flywheel housing near the crankshaft). Inspect the sensor body for physical damage, oil contamination, or loose mounting bolts. Check the wiring harness from sensor to ECM for chafing, cuts, or burn marks—common wear points include areas where the harness contacts the engine block or frame rails.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals (typical specification: 150-300 ohms for magnetic pickup sensors, but consult your service manual). Test continuity in the wiring harness from sensor connector to ECM pins. Check for short circuits to ground by measuring resistance between each wire and chassis ground (should read infinite resistance/open circuit).

Step 3: Sensor Air Gap and Signal Verification Verify the air gap between the sensor tip and flywheel teeth using a feeler gauge (typical spec: 0.5-1.5mm). Remove any metallic debris from the sensor tip. If possible, use Sumitomo diagnostic software or an oscilloscope to monitor the AC voltage signal from the sensor while cranking the engine—you should see a consistent waveform pattern.

Step 4: Component Replacement and Verification For used excavators, if sensor resistance is out of specification or the wiring shows corrosion at connector pins, replace the faulty component. Always apply dielectric grease to connector pins when reassembling to prevent future moisture issues. After repairs, clear the fault code using diagnostic software and perform a test run under load to confirm the fix.

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Disclaimer: This guide provides general troubleshooting information for Fault Code 112. Always consult the official Sumitomo service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues or if you lack proper tools and training.