Sumitomo SH220LC-6 Fault Code 1621: Complete Diagnostic Guide

What is Sumitomo SH220LC-6 Fault Code 1621?

Fault Code 1621 indicates a malfunction in the engine speed sensor circuit or an abnormal signal from the crankshaft position sensor. This code is triggered when the Electronic Control Module (ECM) detects irregular voltage patterns, signal dropouts, or complete loss of communication from the engine speed sensor during operation.

The engine speed sensor is critical for the SH220LC-6's performance because it provides real-time crankshaft position data to the ECM. This information controls fuel injection timing, engine speed regulation, and overall power output. When this sensor fails or sends erratic signals, the excavator's diesel engine cannot maintain proper fuel delivery, leading to performance issues or complete shutdown. For used excavators, this code often appears due to sensor deterioration, wiring harness damage from vibration, or connector corrosion accumulated over thousands of operating hours.

Common Symptoms

When Code 1621 is active on your Sumitomo SH220LC-6, you may experience:

• Engine cranks but fails to start or starts then immediately stalls
• Rough idling and inconsistent RPM fluctuations during operation
• Loss of engine power or inability to reach full operating speed
• Check Engine light illuminated on the instrument panel
• Intermittent engine cutting out during digging or swing operations, especially on older machines with worn components

Potential Causes

The most common technical reasons for Code 1621 on used SH220LC-6 excavators include:

• Failed or worn engine speed sensor due to heat exposure and age-related degradation
• Damaged wiring harness near the sensor mounting location, particularly where the harness contacts the engine block or frame (common rub point on this model)
• Corroded or loose electrical connectors at the sensor or ECM connection points
• Broken or damaged reluctor ring on the crankshaft (rare but possible on high-hour machines)
• ECM internal fault or corrupted software calibration
• Inadequate sensor air gap caused by mounting bracket wear or improper previous installation

How to Troubleshoot and Fix Code 1621

Step 1: Visual Inspection Begin by locating the engine speed sensor on the flywheel housing (driver's side of engine). Inspect the wiring harness for obvious damage, abrasion, or contact points with hot engine components. Check the electrical connector for corrosion, bent pins, or moisture intrusion—common issues in used excavators operating in harsh environments.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. The typical resistance should be between 150-300 ohms (consult your service manual for exact specifications). Also check for continuity in the wiring from sensor to ECM, and verify there's no short to ground. Test signal voltage while cranking—you should see an AC voltage signal (typically 0.5-5V AC).

Step 3: Sensor Air Gap Verification Check the air gap between the sensor tip and reluctor ring using a feeler gauge. The proper gap is typically 0.5-1.5mm. On used machines, mounting bracket wear can increase this gap beyond specification, causing intermittent signal loss.

Step 4: Component Replacement and Verification If testing reveals a faulty sensor, replace it with an OEM or high-quality aftermarket unit. For used excavators, always replace the connector pigtail simultaneously if any corrosion is present. After installation, clear codes using Sumitomo diagnostic software or a compatible scan tool, then run the engine through various RPM ranges to verify proper operation.

Disclaimer: This guide provides general troubleshooting information. Always consult your Sumitomo service manual and consider professional diagnostic assistance for complex electrical issues or if you're unfamiliar with high-pressure diesel systems.