Komatsu PC800LC-8R Fault Code S-2: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code S-2?

Fault Code S-2 on the Komatsu PC800LC-8R indicates a malfunction in the engine speed sensor circuit or an abnormal signal from the crankshaft position sensor system. This code is triggered when the Electronic Control Module (ECM) detects irregular or missing pulses from the engine speed sensor, which monitors crankshaft rotation and timing.

The engine speed sensor is critical for the PC800LC-8R's SAA6D140E-7 engine performance, as it provides essential data for fuel injection timing, engine speed control, and overall combustion management. Without accurate speed sensor readings, the ECM cannot properly regulate engine operations, potentially leading to performance degradation or engine shutdown protection modes.

Common Symptoms

When Code S-2 is active on your PC800LC-8R, operators typically experience:

• Engine cranks but fails to start, or starts with extreme difficulty and rough idling
• Sudden engine stalling during operation, particularly under load conditions
• Monitor panel warning light illuminated with S-2 displayed on the multi-function display
• Loss of engine power or inability to reach rated RPM (approximately 1,950 RPM)
• Intermittent engine cutting out during hydraulic operations or boom/bucket movements

Potential Causes

The most common technical causes for Code S-2 on used PC800LC-8R excavators include:

• Engine speed sensor failure due to internal component degradation or heat exposure over time
• Damaged or corroded wiring harness between the sensor and ECM, particularly at known rub points near the engine mounting brackets
• Contaminated sensor face from metal debris, oil buildup, or coolant intrusion affecting magnetic pickup
• Loose or corroded electrical connectors at the sensor or ECM connection points
• Damaged flywheel ring gear teeth causing irregular signal patterns
• ECM internal fault or corrupted sensor calibration data (less common)

How to Troubleshoot and Fix Code S-2

Step 1: Visual Inspection Begin by locating the engine speed sensor on the flywheel housing (driver's side of the engine block). Inspect the sensor connector for corrosion, bent pins, or moisture intrusion. Check the wiring harness for chafing, particularly where it routes near the engine mounts—a common wear point on used machines.

Step 2: Electrical Testing Using a digital multimeter, measure the sensor's resistance. The engine speed sensor should typically read between 150-300 ohms (consult your service manual for exact specifications). Test continuity from the sensor connector back to the ECM harness connector. Check for voltage supply (typically 8-12V) at the sensor connector with the key on, engine off.

Step 3: Sensor Gap and Physical Condition Verify the air gap between the sensor tip and flywheel ring gear (typically 0.5-1.5mm). Remove the sensor and inspect for metal contamination on the magnetic tip. Clean thoroughly with electrical contact cleaner. Inspect the flywheel teeth for damage using a borescope if necessary.

Step 4: Advanced Diagnostics Connect Komatsu KOMTRAX or compatible diagnostic software to monitor real-time sensor output. Compare the signal pattern against known-good specifications. For used excavators, pay special attention to intermittent connection issues caused by vibration-loosened connectors or work-hardened wiring.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic services for complex electrical issues or ECM programming requirements.