Komatsu PC450-8 Fault Code S-5: Complete Diagnostic Guide

What is Komatsu PC450-8 Fault Code S-5?

Fault Code S-5 on the Komatsu PC450-8 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detected by the Engine Control Module (ECM). This code specifically monitors the oil pressure signal voltage and compares it against predetermined thresholds programmed into the ECM.

The oil pressure monitoring system is critical for the SAA6D125E-5 engine found in the PC450-8, as inadequate lubrication can cause catastrophic bearing failure, turbocharger damage, or complete engine seizure. When S-5 triggers, the ECM may initiate protective measures including engine derate or automatic shutdown to prevent permanent damage.

Common Symptoms

When Code S-5 is active, operators typically experience:

• Oil pressure warning light illuminated on the instrument cluster (red oil can symbol)
• Audible alarm sounding continuously from the cab
• Engine power reduction (derate mode) limiting machine performance to 50-70% capacity
• Automatic engine shutdown 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-5 on used PC450-8 excavators include:

• Failed oil pressure sensor (Komatsu part #6732-81-3140) due to internal diaphragm deterioration
• Damaged wiring harness between sensor and ECM, particularly at the frame flex point near the swing bearing where cable chafing occurs
• Corroded or loose connector pins at the sensor plug (3-pin Deutsch connector)
• Actual low oil pressure caused by worn oil pump, clogged oil filter, or bearing clearance issues
• ECM internal fault in the pressure monitoring circuit (rare but documented in high-hour machines)
• Contaminated engine oil causing sensor membrane fouling

How to Troubleshoot and Fix Code S-5

Step 1: Visual Inspection Begin by checking actual engine oil level and condition. 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 corroded connections. On used excavators, carefully examine the wiring harness for abrasion, particularly where it routes along the frame rails.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Specification should be 50-150 ohms at room temperature. Check supply voltage at the harness connector with ignition on—should read approximately 5 volts. Measure signal wire resistance from sensor connector to ECM pin (consult service manual for specific pin location)—should be less than 5 ohms.

Step 3: Mechanical Verification Install a mechanical oil pressure gauge in the test port to verify actual oil pressure. At operating temperature and idle, pressure should exceed 50 PSI (345 kPa); at rated RPM, expect 85-100 PSI (586-690 kPa). If mechanical pressure is adequate but code persists, replace the pressure sensor. If pressure is low, investigate oil pump wear, filter restriction, or internal engine wear.

Step 4: Connector Service For used machines, clean all connector pins with electrical contact cleaner and apply dielectric grease. Check for terminal tension—loose pins are common failure points after 5,000+ hours.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. Complex repairs should be performed by qualified technicians with proper diagnostic equipment.