What is Komatsu PC100-6 Fault Code S-15?

Fault Code S-15 on the Komatsu PC100-6 indicates a malfunction in the engine oil pressure sensor circuit. This code triggers when the Engine Control Module (ECM) detects abnormal voltage signals from the oil pressure sensor, suggesting either sensor failure, wiring issues, or actual low oil pressure conditions.

The oil pressure monitoring system is critical for protecting the Komatsu SAA4D102E engine from catastrophic damage. This sensor provides real-time feedback to the ECM, allowing it to alert operators and initiate protective shutdowns before bearing seizure or engine failure occurs. On used PC100-6 excavators, this code frequently appears due to sensor degradation or harness deterioration from years of vibration and heat exposure.

Common Symptoms

• Intermittent or constant oil pressure warning light illumination on the instrument cluster
• Audible alarm sounding even when engine oil level is correct and engine sounds normal
• Engine derate mode or automatic shutdown in severe cases to prevent damage
• Erratic gauge readings showing fluctuating oil pressure despite stable engine operation
• Difficulty starting or extended cranking times due to ECM safety protocols

Potential Causes

The S-15 code typically stems from sensor-related failures common in older machinery. The oil pressure sensor itself (part number 7861-93-1650) frequently fails after 5,000+ operating hours due to internal diaphragm fatigue. Wiring harness chafing is another prevalent issue—the harness routing near the engine block on PC100-6 models creates a known rub point against the fuel filter bracket.

Connector corrosion at the sensor plug is extremely common in machines exposed to moisture or stored outdoors. The three-pin connector accumulates dirt and oxidation, creating intermittent contact. Additionally, ECM ground wire degradation can cause phantom codes as poor grounding affects sensor voltage reference signals.

How to Troubleshoot and Fix Code S-15

Step 1: Visual Inspection and Basic Checks Before replacing components, verify actual engine oil level and condition. Inspect the oil pressure sensor (located on the left side of the engine block below the injection pump) for oil leaks, damaged wiring, or loose connections. Check the harness routing for abrasion points, especially where it passes near the fuel filter housing.

Step 2: Electrical Testing Using a digital multimeter, perform resistance testing on the sensor. Disconnect the three-pin connector and measure resistance between sensor terminals with the engine off—readings should be 100-300 ohms at room temperature. Test supply voltage at the harness connector with ignition on; you should see approximately 5V on the reference wire. Measure continuity from sensor ground to battery negative.

Step 3: Sensor and Harness Verification If voltage and ground are correct but the code persists, install a known-good oil pressure sensor to eliminate sensor failure. For used excavators, closely examine the connector pins for corrosion—cleaning with electrical contact cleaner often resolves intermittent codes. Replace damaged harness sections rather than attempting repairs, as vibration will reopen soldered joints.

Step 4: ECM and Mechanical Verification If electrical testing proves inconclusive, connect Komatsu diagnostic software (KOMTRAX or aftermarket equivalent) to monitor live sensor data. Compare displayed oil pressure against a mechanical test gauge installed at the sensor port. Significant discrepancies indicate sensor inaccuracy. Check ECM software version, as outdated firmware can cause false codes.

For persistent issues on high-hour machines, inspect the engine oil pump and pressure relief valve for wear, as actual mechanical oil pressure problems will trigger S-15 codes legitimately.

---

Disclaimer: This guide provides general troubleshooting information. Always consult qualified diesel mechanics and reference the official Komatsu PC100-6 service manual for precise specifications and safety procedures before performing repairs.