Komatsu PC750-7 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code S-6?

Fault Code S-6 on the Komatsu PC750-7 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 from the sensor to the ECM, ensuring adequate lubrication reaches critical engine components.

This fault is critical for the PC750-7's SAA6D140E-5 engine because insufficient oil pressure can lead to catastrophic bearing failure, turbocharger damage, or complete engine seizure. The ECM uses this sensor data to protect the engine by triggering warnings or initiating automatic shutdown sequences when pressure falls below safe operating thresholds.

Common Symptoms

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

• Engine oil pressure warning light illuminated on the instrument cluster (red oil can symbol)
• Audible alarm sounding continuously in the cab
• Automatic engine derate or shutdown after a brief warning period (typically 30-60 seconds)
• Reduced hydraulic performance as engine RPM is limited by protective protocols
• Visible low oil pressure gauge reading on the monitor panel (below 2.0 kg/cm² at operating temperature)

Potential Causes

The most common technical causes for S-6 on used PC750-7 excavators include:

• Failed engine oil pressure sensor (common failure point after 8,000+ hours)
• Damaged or corroded wiring harness between sensor and ECM, particularly at the engine valley routing area where heat and vibration cause insulation breakdown
• Actual low engine oil pressure due to worn oil pump, clogged oil filter, or bearing clearance issues
• Contaminated engine oil or incorrect viscosity affecting pressure readings
• Loose or corroded electrical connectors at the sensor or ECM interface
• ECM internal fault (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code S-6

Step 1: Visual Inspection Check engine oil level using the dipstick—ensure oil is at proper level and inspect for contamination or metal particles. Examine the oil pressure sensor (located on the engine block's left side) for physical damage, oil leaks, or loose connections. Inspect the wiring harness from sensor to ECM for chafing, burns, or rodent damage.

Step 2: Electrical Testing Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across sensor terminals. Typical resistance should be 50-150 ohms at room temperature (consult service manual for exact specifications). Check for 5-volt reference voltage from the ECM at the connector with ignition on. Inspect connector pins for corrosion—a common issue in used excavators operating in humid environments.

Step 3: Pressure Verification Install a mechanical oil pressure gauge at the sensor port to verify actual engine oil pressure. At normal operating temperature (80°C), pressure should read 3.5-4.5 kg/cm² at rated RPM. If mechanical gauge shows proper pressure but code persists, replace the oil pressure sensor. If actual pressure is low, investigate oil pump wear, filter restriction, or internal engine wear.

Step 4: Harness and Connector Service For used machines, carefully inspect the entire sensor harness for wear points where it contacts the engine block or frame. Clean all connector terminals with electrical contact cleaner and apply dielectric grease. Check for proper harness routing and secure with new tie wraps away from heat sources.

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