What is Komatsu PC120-6 Fault Code S-16?

Fault Code S-16 on the Komatsu PC120-6 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detection. This code triggers when the Engine Control Module (ECM) receives readings outside the normal operating parameters from the oil pressure sensor, typically below 0.5 kg/cm² at rated engine speed or detecting electrical circuit abnormalities.

This fault is critical for the PC120-6's 6D95L engine because inadequate oil pressure monitoring can lead to catastrophic engine damage. The oil pressure system ensures proper lubrication of crankshaft bearings, camshaft assemblies, and hydraulic valve train components. When this code activates, the machine may enter derate mode to protect internal engine components from insufficient lubrication.

Common Symptoms

• Engine warning lamp illuminates on the instrument cluster, often accompanied by an audible alarm
• Engine power reduction (derate) limiting machine to approximately 70% rated output
• Hydraulic system sluggishness due to reduced engine RPM capability
• Intermittent or constant low oil pressure warning, even after recent oil changes
• Hard starting or rough idle conditions, particularly when engine is cold

Potential Causes

The most frequent causes on used PC120-6 excavators include:

• Oil pressure sensor failure due to age-related diaphragm degradation or internal sensor contamination
• Wiring harness chafing at known rub points near the engine mounting bracket (common on machines with 5,000+ hours)
• Connector corrosion on the 3-pin sensor connector, especially on machines operating in wet or coastal environments
• Low engine oil level or using incorrect viscosity oil (20W-40 is specified for this model)
• ECM ground connection deterioration at the battery negative terminal or chassis ground points
• Worn oil pump delivering insufficient pressure at operating temperature (typically on high-hour machines)

How to Troubleshoot and Fix Code S-16

Step 1: Visual Inspection and Oil Verification Check actual engine oil level with machine on level ground. Verify oil meets Komatsu specifications (API CF or higher, SAE 10W-30 or 15W-40 depending on ambient temperature). Inspect the oil pressure sensor (located on the left side of the cylinder block) for physical damage or oil leaks indicating internal diaphragm failure.

Step 2: Electrical Circuit Testing Using a digital multimeter, check sensor resistance. Disconnect the sensor connector and measure resistance between the sensor terminal and sensor body—it should read 50-150 ohms at room temperature. Check wiring continuity from the sensor connector back to ECM pin C-23. Inspect the harness routing along the engine valley for signs of insulation wear or wire exposure.

Step 3: Sensor Signal Verification With the engine running at operating temperature, backprobe the sensor connector using a multimeter set to DC voltage. Normal readings should be 0.5-4.5V proportional to oil pressure. If voltage remains constant regardless of RPM changes, replace the sensor. For used excavators, always apply dielectric grease to connector pins during reassembly to prevent future corrosion.

Step 4: Mechanical Pressure Testing If electrical tests pass but the code persists, install a mechanical oil pressure gauge at the sensor port. Normal pressure should be 3.5-4.5 kg/cm² at 2,000 RPM when warm. Low readings indicate oil pump wear, clogged oil passages, or excessive bearing clearances requiring internal engine inspection.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex engine issues.