Komatsu PC800LC-8R Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC800LC-8R Fault Code S-6?

Fault Code S-6 on the Komatsu PC800LC-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 engine oil pressure sensor sends a continuous voltage signal to the ECM, which interprets this data to ensure adequate lubrication throughout the engine's critical components. On the PC800LC-8R's SAA6D140E-7 engine, maintaining proper oil pressure is essential for protecting turbocharger bearings, main bearings, and camshaft components. When this code triggers, the machine may enter a protective derate mode to prevent catastrophic engine damage.

Common Symptoms

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

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Automatic engine power reduction (derate) limiting machine performance to 70-80% capacity
• Low oil pressure warning displayed on the multi-function monitor screen
• Unusual engine knocking or ticking sounds if actual oil pressure is critically low
• Engine shutdown in severe cases where pressure drops below minimum safe operating levels

Potential Causes

The most common technical reasons for Code S-6 on used PC800LC-8R excavators include:

• Failed oil pressure sensor (Komatsu part #6754-21-6140) due to internal diaphragm deterioration
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine mount
• Corroded or loose electrical connectors at the sensor terminal or ECM pins
• Low engine oil level or use of incorrect viscosity oil for operating conditions
• Worn oil pump or clogged oil filter restricting flow in high-hour machines
• ECM calibration issues or software glitches requiring reprogramming
• Actual low oil pressure caused by worn main/rod bearings in excavators exceeding 8,000 hours

How to Troubleshoot and Fix Code S-6

Step 1: Initial Visual Inspection Begin by checking the 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. Examine the wiring harness for chafing, cuts, or signs of rodent damage.

Step 2: Electrical Testing Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across the sensor terminals. At room temperature, resistance should typically read 50-150 ohms (consult your service manual for exact specifications). Check for supply voltage at the harness connector—you should see approximately 5 volts from the ECM. Measure signal wire continuity from the sensor connector back to ECM pin locations.

Step 3: Mechanical Verification Install a mechanical oil pressure gauge into the sensor port to verify actual oil pressure. At normal operating temperature and idle, pressure should read 30-50 PSI minimum; at high idle (1,800 RPM), expect 60-85 PSI. If mechanical pressure is adequate but the code persists, replace the oil pressure sensor. For used excavators, always apply dielectric grease to connector pins before reassembly to prevent future corrosion.

Step 4: Advanced Diagnostics Connect Komatsu diagnostic software (KTEC or equivalent) to read live sensor data and compare voltage output against actual pressure readings. Clear the fault code and perform a regeneration test while monitoring parameters. If codes return immediately, inspect the ECM ground connections and check for ECM internal faults.

---

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number. If you're uncomfortable performing electrical diagnostics or if mechanical oil pressure is confirmed low, consult a certified Komatsu technician to prevent engine damage.