Komatsu PC450LC-6 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC450LC-6 Fault Code S-6?

Fault Code S-6 on the Komatsu PC450LC-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, typically below 0.5 bar at idle or during operation.

This fault is critical for the PC450LC-6's SAA6D125E-3 engine because inadequate oil pressure can lead to catastrophic bearing failure, turbocharger damage, and complete engine seizure. The monitoring system is designed to protect the engine by alerting operators before irreversible damage occurs. In used excavators, this code often appears due to sensor degradation or actual mechanical wear in the lubrication system.

Common Symptoms

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

• Oil pressure warning light illuminated on the instrument cluster (red oil can symbol)
• Audible alarm sounding continuously during operation
• Engine derate mode activated, limiting RPM to approximately 1,200-1,400 to prevent damage
• Automatic engine shutdown in severe cases after a brief warning period (typically 30 seconds)
• Erratic oil pressure gauge readings or gauge stuck at zero despite engine running

Potential Causes

The most common technical causes for Code S-6 on used PC450LC-6 excavators include:

• Failed oil pressure sensor (Komatsu part #6732-81-3140) due to internal diaphragm deterioration
• Damaged sensor wiring harness at known rub points near the engine mount brackets and fuel filter housing
• Corroded or loose electrical connectors at the sensor terminal (3-pin connector)
• Actual low oil pressure caused by worn oil pump, clogged oil filter, or excessive bearing clearances
• Low engine oil level or use of incorrect viscosity oil for operating conditions
• ECM calibration issues or corrupted software (rare but documented in 2001-2003 production units)

How to Troubleshoot and Fix Code S-6

Step 1: Verify Actual Oil Pressure Install a mechanical oil pressure gauge directly into the engine block test port (located near the oil filter housing). Run the engine and compare readings to specifications: 3.5-4.5 bar at 2,000 RPM when warm. If mechanical pressure is normal, the issue is electrical; if low, investigate mechanical causes first.

Step 2: Inspect Sensor and Wiring Locate the oil pressure sensor on the left side of the engine block below the fuel injection pump. Disconnect the 3-pin connector and inspect for corrosion, oil contamination, or pushed-back pins. On used excavators, check the wiring harness for abrasion damage where it contacts the engine mount—this is a known failure point on PC450LC-6 models with over 8,000 hours.

Step 3: Test Sensor Resistance Using a digital multimeter, measure sensor resistance between the signal pin and ground. Specifications should read 50-150 ohms at room temperature. Also check for 5-volt reference voltage from the ECM at the connector with ignition on. If voltage is absent, trace wiring back to the ECM for breaks or shorts.

Step 4: Check ECM Inputs Connect Komatsu diagnostic software (KOMTRAX Plus or compatible) to monitor real-time oil pressure values. Compare sensor readings to mechanical gauge. A variance greater than 0.5 bar indicates sensor replacement is needed. Clear codes and perform a stationary regeneration test to verify repair.

For used excavators, always inspect oil filter condition, check for metal particles indicating bearing wear, and verify proper oil viscosity (15W-40 for standard conditions). Replace corroded connectors with dielectric grease application to prevent future corrosion.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC450LC-6 service manual and consider professional assessment by certified technicians for complex repairs. Improper diagnosis may result in equipment damage or safety hazards.