What is Sumitomo SH300-6 Fault Code 1112?

Fault Code 1112 on the Sumitomo SH300-6 excavator indicates an Engine Speed Sensor (ESS) circuit malfunction or abnormal signal deviation. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an inconsistent or out-of-range signal from the engine speed sensor, which monitors crankshaft rotation speed and timing.

The engine speed sensor is critical for the SH300-6's fuel injection timing, governor control, and overall engine performance management. When this sensor fails or sends erratic signals, the ECM cannot properly regulate fuel delivery or coordinate with the hydraulic system's load-sensing capabilities. On used excavators, this code often appears due to sensor degradation, wiring harness damage from vibration, or connector corrosion—common issues in machines with 5,000+ operating hours.

Common Symptoms

When Code 1112 is active on your Sumitomo SH300-6, you may experience:

• Intermittent engine stalling or failure to start, especially during cold starts
• Erratic engine RPM fluctuations under load or at idle
• Loss of hydraulic power or sluggish boom/arm response due to improper engine-pump coordination
• Engine warning light illuminated on the dashboard or monitor panel
• Reduced engine performance with possible activation of derate mode limiting maximum RPM

Potential Causes

The most common technical causes for Code 1112 on used SH300-6 excavators include:

• Faulty engine speed sensor due to internal component wear or magnetic pickup degradation
• Damaged wiring harness from rubbing against engine components, particularly near the flywheel housing where the sensor mounts
• Corroded or loose electrical connectors at the sensor or ECM interface
• ECM software glitches or calibration drift in older control modules
• Damaged flywheel ring gear causing irregular signal patterns
• Excessive air gap between the sensor tip and flywheel teeth due to improper installation or sensor bracket wear

How to Troubleshoot and Fix Code 1112

Step 1: Visual Inspection Begin by locating the engine speed sensor on the flywheel housing (typically on the transmission side of the engine block). Inspect the wiring harness for signs of abrasion, heat damage, or pinch points. Check the electrical connector for corrosion, bent pins, or moisture intrusion—common in used excavators operating in harsh environments.

Step 2: Sensor Air Gap Verification Using a feeler gauge, verify the air gap between the sensor tip and flywheel teeth is within specification (typically 0.5-1.5mm for Sumitomo models). Excessive gap prevents proper signal generation. Clean any metal debris or oil buildup from the sensor face.

Step 3: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across the sensor terminals (typical range: 150-300 ohms, but verify with service manual specifications). Test the wiring harness continuity from sensor to ECM, checking for opens or shorts to ground. Measure supply voltage at the connector (should be approximately 5-12V DC depending on system design).

Step 4: Signal Testing (Dynamic) Reconnect the sensor and use a diagnostic laptop with Sumitomo-compatible software or an oscilloscope to monitor the AC voltage signal while cranking the engine. A healthy sensor produces a consistent waveform with amplitude increasing with RPM.

Step 5: Component Replacement If testing confirms sensor failure, replace with an OEM or high-quality aftermarket engine speed sensor. For used excavators, always apply dielectric grease to connector terminals to prevent future corrosion. Clear codes with diagnostic software and perform a test run under load.

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Disclaimer: This guide provides general troubleshooting information for Code 1112. Always consult the official Sumitomo SH300-6 service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.