Komatsu PC450-6 Fault Code S-8: Complete Diagnostic Guide

What is Komatsu PC450-6 Fault Code S-8?

Fault Code S-8 on the Komatsu PC450-6 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 PC450-6'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-8 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 S-8 on used PC450-6 excavators include:

• Failed oil pressure sensor (Komatsu part #6732-81-3140) due to internal diaphragm deterioration
• Damaged sensor wiring harness at the rub point near the engine mount bracket—a known wear location on this model
• Corroded or loose electrical connectors at the sensor or ECM interface
• Actual low oil pressure caused by worn oil pump, clogged oil filter, or bearing clearance issues
• Low engine oil level or use of incorrect viscosity oil
• ECM calibration issues or internal ECM fault (less common)

How to Troubleshoot and Fix Code S-8

Step 1: Visual Inspection Check engine oil level using the dipstick—ensure oil is at the proper mark and appears clean. Inspect the oil pressure sensor (located on the left side of the engine block near the oil filter housing) for physical damage, oil leaks, or loose connections. On used excavators, carefully examine the wiring harness for chafing, especially where it contacts the engine mount.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. Specifications should read approximately 50-150 ohms at room temperature (consult service manual for exact values). Check for 5-volt reference voltage at the harness connector with ignition on. Inspect connector pins for corrosion or bent terminals—common issues in machines with 5,000+ operating hours.

Step 3: Mechanical Verification Install a mechanical oil pressure gauge at the sensor port to verify actual oil pressure. At operating temperature, pressure should read 3.5-4.5 bar at rated RPM. If mechanical pressure is adequate but the code persists, replace the sensor. If pressure is low, investigate the oil pump, relief valve, or internal engine wear.

Step 4: Clear Code and Monitor After repairs, clear the fault code using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool. Operate the machine through various load conditions and monitor for code recurrence.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. If internal engine wear is suspected, professional evaluation by a certified heavy equipment technician is strongly recommended before continued operation.