Komatsu PC800-8R Fault Code S-10: Complete Diagnostic Guide

What is Komatsu PC800-8R Fault Code S-10?

Fault Code S-10 on the Komatsu PC800-8R 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 Komatsu KOMTRAX system.

The S-10 code affects the engine's lubrication monitoring system, which is critical for protecting the SAA6D170E-5 engine found in the PC800-8R. When this code activates, the ECM may initiate protective measures to prevent catastrophic engine damage. For used excavators operating with higher hours, this fault requires immediate attention as inadequate oil pressure can lead to bearing failure, turbocharger damage, and complete engine seizure.

Common Symptoms

When Code S-10 is active, operators typically experience:

• Engine oil pressure warning light illuminated on the monitor panel (red oil can symbol)
• Audible alarm sounding continuously from the cab
• Engine derate mode activated, limiting RPM to 1200-1400 range to protect components
• Automatic engine shutdown after 30-60 seconds if pressure remains critically low
• Visible low oil pressure reading on the digital gauge (below 50 kPa at idle or 200 kPa at rated speed)

Potential Causes

The most common technical causes for S-10 on used PC800-8R excavators include:

• Failed oil pressure sensor (Komatsu part #6754-21-6140) due to internal diaphragm deterioration
• Damaged sensor wiring harness at known rub points near the engine mount brackets
• Corroded or loose electrical connectors at the sensor or ECM interface (C-connector series)
• Actual low oil pressure caused by worn oil pump, clogged oil filter, or bearing clearance issues
• ECM calibration drift or software corruption in machines with 8,000+ operating hours
• Contaminated engine oil causing sensor membrane fouling

How to Troubleshoot and Fix Code S-10

Step 1: Initial Visual Inspection Check engine oil level using the dipstick—ensure oil is at the proper level and not contaminated with coolant or fuel. 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.

Step 2: Electrical Circuit Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. The sensor should read approximately 50-150 ohms at room temperature. Check for supply voltage at the harness connector—you should see 5.0V ± 0.5V from the ECM. Inspect the signal wire (typically green/white) and ground wire for continuity and resistance below 5 ohms.

Step 3: Mechanical Pressure Verification Install a mechanical oil pressure gauge in place of the sensor to verify actual oil pressure. At operating temperature, pressure should read 300-450 kPa at rated RPM and minimum 100 kPa at idle. If mechanical pressure is adequate but the code persists, replace the sensor.

Step 4: Used Equipment Considerations For used excavators, thoroughly inspect the wiring harness from sensor to ECM for abrasion damage where it passes near the engine mount and hydraulic lines—a common failure point on PC800 models. Clean all connector pins with electrical contact cleaner and apply dielectric grease. Check for oil contamination inside connectors, which indicates seal failure.

Step 5: Component Replacement and Verification Replace the oil pressure sensor with a genuine Komatsu part or verified OEM equivalent. Clear the fault code using Komatsu diagnostic software (KTEC) or compatible scan tool. Run the engine through operating temperature and verify the code does not return.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex issues. Improper repairs may void warranties or cause equipment damage.