What is Komatsu PC130-6 Fault Code S-2?

Fault Code S-2 on the Komatsu PC130-6 indicates a malfunction in the engine speed sensor circuit or signal abnormality. This code specifically relates to the engine's revolution sensor system, which monitors crankshaft speed and provides critical data to the Engine Control Module (ECM).

The engine speed sensor generates electrical pulses that allow the ECM to calculate precise RPM, control fuel injection timing, and manage overall engine performance. For the PC130-6's 4D95LE diesel engine, this signal is essential for proper fuel delivery and smooth operation. When this sensor circuit fails or provides erratic signals, the ECM cannot accurately control engine functions, potentially leading to performance degradation or shutdown protection modes.

Common Symptoms

• Engine will not start or cranks but fails to fire due to ECM not detecting rotation
• Erratic engine RPM fluctuation or unexpected surging during operation
• Intermittent stalling especially at idle or under load conditions
• Monitor panel displays the S-2 error code on the control panel
• Reduced engine power or limp mode activation to prevent potential damage

Potential Causes

The most common causes for S-2 codes on used PC130-6 excavators include:

• Engine speed sensor failure due to internal component degradation or coil winding breakdown
• Wiring harness damage from rubbing against the engine block or flywheel housing—a known wear point on this model
• Connector corrosion at the sensor plug, especially in machines exposed to water or high humidity environments
• Air gap issue between the sensor tip and flywheel teeth caused by improper installation or mounting bracket wear
• ECM malfunction (less common) where the module cannot properly process the sensor signal
• Damaged flywheel teeth creating irregular signal patterns from impact or metal fatigue

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 4D95LE engine). Inspect the wiring harness for visible abrasion, cuts, or rubbing damage—particularly where it routes near moving components. Check the connector for moisture, corrosion, or bent pins. For used excavators, examine the mounting area for oil leaks that may have contaminated the sensor.

Step 2: Sensor Testing Disconnect the sensor connector and measure resistance across the sensor terminals using a digital multimeter. The PC130-6 speed sensor should typically read between 150-300 ohms (consult your service manual for exact specifications). Check the air gap between the sensor tip and flywheel teeth—it should be 0.5-1.5mm. Use a feeler gauge to verify proper clearance.

Step 3: Signal Verification Reconnect the sensor and use Komatsu KOMTRAX diagnostic software or a compatible scan tool to monitor live sensor data while cranking. The signal should show consistent pulses. If voltage output is erratic or absent, replace the sensor. Before installing new parts on used machines, clean all mounting surfaces and apply dielectric grease to connectors to prevent future corrosion.

Step 4: Harness and ECM Check If the sensor tests good, inspect wiring continuity from sensor to ECM pin (check wiring diagrams). Verify no shorts to ground. In rare cases, ECM replacement may be necessary if internal circuitry has failed.

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