Komatsu PC100-6 Fault Code E104: Technical Guide

What is Komatsu PC100-6 Fault Code E104?

Fault Code E104 on the Komatsu PC100-6 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low oil pressure detection. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) receives signals outside the normal operating parameters from the oil pressure sensor, typically below 0.5V or above 4.8V at the sensor input.

This code is critical because proper oil pressure monitoring protects the Komatsu 4D95LE diesel engine from catastrophic bearing and camshaft damage. When E104 activates, the ECM may initiate protective measures including power derate or automatic shutdown to prevent engine seizure.

Common Symptoms

When Code E104 is active, operators typically experience:

• Oil pressure warning lamp illuminated on the instrument cluster (red oil can symbol)
• Engine power reduction (derate mode) limiting machine to 50-70% normal output
• Audible warning alarm from the cab monitoring system
• Hydraulic system sluggishness due to reduced engine RPM in protection mode
• Intermittent code appearance during cold starts or under heavy load conditions

Potential Causes

The most common technical causes for E104 on used PC100-6 excavators include:

• Oil pressure sensor failure (typical lifespan 3,000-5,000 operating hours)
• Wiring harness damage at the sensor connector near the oil filter housing, where engine vibration causes wire abrasion
• Corroded or oil-contaminated connector pins at the 3-pin sensor plug
• Low actual engine oil pressure due to worn oil pump, clogged oil filter, or bearing clearance issues
• ECM voltage supply problem affecting the 5V reference circuit to the sensor
• Damaged sensor mounting threads causing oil leaks and pressure loss

How to Troubleshoot and Fix Code E104

Step 1: Visual Inspection Locate the oil pressure sensor on the left side of the engine block, near the oil filter. On used excavators, carefully inspect the wiring harness for chafing against the engine mount bracket—a known wear point on PC100-6 models. Check the connector for oil contamination, bent pins, or corrosion.

Step 2: Electrical Testing Using a digital multimeter, backprobe the sensor connector with the ignition ON, engine OFF. Verify 5V reference voltage on the signal wire (typically gray wire). Measure sensor resistance: should read 240-360 ohms at 20°C. If readings are out of specification or show infinite resistance, replace the sensor.

Step 3: Mechanical Verification Install a mechanical oil pressure gauge at the sensor port. Start the engine and verify actual oil pressure: should read 280-420 kPa (40-60 PSI) at normal operating temperature and idle speed. If mechanical pressure is correct but the code persists, the sensor is faulty. If pressure is low, investigate oil pump wear, filter restriction, or engine bearing clearances.

Step 4: Harness Continuity Check Disconnect both the sensor and ECM connector C2 (behind the right-side panel). Check continuity between sensor signal pin and ECM pin 23. Resistance should be below 2 ohms. Check for shorts to ground (should be infinite resistance). Repair or replace harness sections showing damage.

Disclaimer: This guide provides general diagnostic procedures. For used excavators with complex electrical issues or low mechanical oil pressure, consult a certified Komatsu technician or diesel specialist to prevent misdiagnosis and costly component replacement.