Komatsu PC70-8 Fault Code S-6: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code S-6?

Fault Code S-6 on the Komatsu PC70-8 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detected by the Electronic Control Module (ECM). This code specifically monitors the oil pressure sensor signal voltage and actual pressure readings to protect the engine from catastrophic damage due to inadequate lubrication.

The oil pressure sensor sends continuous voltage signals to the ECM, which interprets these readings to ensure proper engine lubrication. When the signal falls outside predetermined parameters or actual pressure drops below safe thresholds, the S-6 code triggers. This is critical for the PC70-8's 4D95LE engine, as insufficient oil pressure can lead to bearing failure, piston seizure, and complete engine destruction within minutes of operation.

Common Symptoms

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

• Oil pressure warning light illuminated on the instrument panel (red oil can symbol)
• Audible alarm or buzzer sounding continuously during operation
• Engine derate mode or automatic shutdown if pressure remains critically low
• Rough idle or unusual engine knocking sounds indicating lubrication issues
• Reduced hydraulic performance as the ECM limits engine RPM to prevent damage

Potential Causes

The most common technical reasons for S-6 codes on used PC70-8 excavators include:

• Faulty oil pressure sensor (common failure point after 5,000+ hours)
• Low engine oil level due to leaks or consumption
• Worn oil pump unable to maintain adequate pressure
• Damaged wiring harness between sensor and ECM, especially near engine mount points where vibration causes wire chafing
• Corroded or loose electrical connectors at the sensor or ECM terminals
• Clogged oil filter restricting flow and reducing pressure
• ECM software glitches or internal ECM failure (less common)

How to Troubleshoot and Fix Code S-6

Step 1: Verify Actual Oil Pressure Install a mechanical oil pressure gauge directly into the engine block test port. Start the engine and compare readings against Komatsu specifications (typically 29-43 PSI at idle, 57-85 PSI at rated RPM). If mechanical pressure is normal, the issue is electrical.

Step 2: Inspect Oil Pressure Sensor and Wiring Locate the oil pressure sensor on the engine block (driver's side, near oil filter). Disconnect the sensor connector and inspect for corrosion, oil contamination, or bent pins—common issues in used excavators. Check the wiring harness along its entire length for abrasion points, particularly where it contacts the engine block or frame. Use a multimeter to test sensor resistance (typically 50-150 ohms) and signal voltage (0.5-4.5V range).

Step 3: Test ECM Signal and Replace Components With ignition on (engine off), backprobe the sensor connector to verify 5-volt reference voltage from the ECM. If voltage is absent, trace wiring to the ECM connector and check for continuity. Replace the sensor if resistance/voltage tests fail. For used machines, always apply dielectric grease to connectors during reassembly to prevent future corrosion.

Step 4: Address Mechanical Issues If mechanical pressure is low, check engine oil level and condition first. Replace the oil filter and retest. Persistent low pressure requires oil pump inspection or engine teardown to assess bearing clearances.

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual and consider professional assistance for complex repairs, especially on used equipment with unknown maintenance history.