What is Kobelco SK200-6 Fault Code A-2?

Fault Code A-2 on the Kobelco SK200-6 excavator indicates a malfunction in the engine speed sensor circuit or an abnormal engine speed signal being transmitted to the machine's Electronic Control Module (ECM). This code specifically relates to the communication between the engine's speed sensor (often a magnetic pickup sensor) and the controller, which monitors crankshaft rotation to manage fuel injection timing, engine performance, and safety shutdowns.

This fault is critical for the SK200-6 because the ECM relies on accurate engine speed data to optimize the Isuzu 6BG1 engine's performance. Without proper speed signal input, the machine may experience reduced power output, irregular idling, or complete engine shutdown to prevent damage. For owners of used excavators, this code often appears due to sensor degradation, wiring corrosion, or connector issues common in machines with high operating hours.

Common Symptoms

When Code A-2 is active on your Kobelco SK200-6, you may notice:

• Engine warning light illuminated on the instrument panel or display
• Erratic or unstable idle speed, with RPMs fluctuating unexpectedly
• Sudden engine stalling during operation or difficulty restarting
• Loss of engine power or failure to reach normal operating RPM
• Engine shutdown after a brief period of running, especially under load

Potential Causes

The most common technical reasons for Code A-2 appearing on used SK200-6 excavators include:

• Failed or damaged engine speed sensor (magnetic pickup sensor) due to heat exposure or mechanical wear
• Corroded or loose wiring connections at the sensor connector or ECM harness plug
• Damaged wiring harness caused by rubbing against the engine block, frame components, or hydraulic lines—a known issue in older Kobelco models
• Contaminated sensor face with metal shavings, oil buildup, or debris affecting magnetic field detection
• Faulty ECM or internal controller circuit failure (less common but possible in high-hour machines)
• Incorrect air gap between the speed sensor and the crankshaft tone ring/flywheel teeth

How to Troubleshoot and Fix Code A-2

Step 1: Visual Inspection Begin by locating the engine speed sensor on the Isuzu 6BG1 engine (typically mounted near the flywheel housing or crankshaft pulley). Inspect the sensor body for physical damage, cracks, or oil contamination. Check the wiring harness for signs of abrasion, especially where it routes near hot engine components or sharp edges. On used excavators, harness wear at mounting brackets is extremely common—look for exposed copper wire or melted insulation.

Step 2: Connector and Resistance Testing Disconnect the speed sensor connector and inspect pins for corrosion, bent contacts, or moisture intrusion. Using a digital multimeter, measure the sensor's resistance across its terminals—typical readings should be between 150-300 ohms (consult your service manual for exact specifications). If readings are infinite (open circuit) or zero (short circuit), the sensor has failed and requires replacement.

Step 3: Signal Voltage Check Reconnect the sensor and use a multimeter set to AC voltage to check signal output while cranking the engine. You should see a fluctuating AC voltage (typically 0.5-3V AC) indicating proper magnetic pulse generation. No voltage signal indicates sensor failure or incorrect air gap. For the SK200-6, the proper air gap between sensor tip and flywheel teeth should be 0.5-1.5mm—adjust if necessary using shims.

Step 4: Wiring Continuity Test Trace the wiring from the sensor back to the ECM connector. Test continuity on both signal wires and check for shorts to ground. Pay special attention to areas where the harness passes through the engine bay firewall or near the hydraulic pump—these are known rub points on used SK200-6 machines.

Step 5: Clear Code and Test After repairs, use Kobelco diagnostic software or a compatible scan tool to clear the fault code from ECM memory. Start the engine and monitor for code reoccurrence. Perform a load test by operating hydraulic functions to ensure stable engine speed under demand.

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Disclaimer: This guide provides general troubleshooting information for the Kobelco SK200-6. Always consult the manufacturer's service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may lead to further damage or safety hazards.