Komatsu PC400-6 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC400-6 Fault Code S-6?

Fault Code S-6 on the Komatsu PC400-6 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detected by the monitoring system. This code is generated when the Electronic Control Module (ECM) receives signals outside the normal operating parameters from the oil pressure sensor, or when actual oil pressure drops below the manufacturer's specified threshold during engine operation.

This fault is critical for the PC400-6 because inadequate oil pressure can lead to catastrophic engine damage. The SAA6D125E-3 engine in this model relies on consistent oil pressure to lubricate bearings, pistons, and turbocharger components. When S-6 triggers, the machine's protection systems may activate to prevent severe mechanical failure.

Common Symptoms

When Code S-6 is active, operators typically experience:

• Engine warning light illuminated on the instrument panel, often accompanied by an audible alarm
• Automatic engine derate or shutdown in severe cases, limiting machine operation
• Visible low oil pressure gauge reading on the dashboard (below 2.5 kg/cm² at rated RPM)
• Unusual engine noise such as knocking or ticking, indicating insufficient lubrication
• Intermittent code activation during cold starts or under heavy load conditions

Potential Causes

The most common technical causes for S-6 on used PC400-6 excavators include:

• Faulty oil pressure sensor (common failure point after 8,000+ operating hours)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector points near the engine block
• Low engine oil level or use of incorrect viscosity grade oil
• Worn oil pump or internal engine wear causing actual pressure loss
• Clogged oil filter or restricted oil passages due to sludge buildup
• ECM calibration issues or internal ECM faults (less common but possible in older units)

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Check engine oil level using the dipstick—ensure oil is at the proper level and appears clean. Inspect the oil pressure sensor (located on the left side of the engine block) and its wiring harness for physical damage, corrosion, or oil contamination on connectors. On used excavators, pay special attention to harness routing where it may rub against the engine or frame.

Step 2: Sensor Circuit Testing Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 50-150 ohms at room temperature). Check for continuity in the wiring from sensor to ECM, and verify no short to ground exists (should read infinite resistance).

Step 3: Actual Pressure Verification Install a mechanical oil pressure gauge in place of the sensor to verify actual engine oil pressure. At normal operating temperature and rated RPM (2,000 RPM), pressure should read 4.5-5.5 kg/cm². If mechanical pressure is adequate but the code persists, replace the oil pressure sensor. If pressure is low, investigate the oil pump, bearings, or internal engine wear.

Step 4: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX or PC-based tools) to read live sensor data and verify ECM functionality. Clear codes after repairs and perform a test run under load to confirm the fix.

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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 engine issues.