Komatsu PC750-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC750-7 Fault Code E-31?

Fault Code E-31 on the Komatsu PC750-7 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detection. This code is triggered when the Electronic Control Module (ECM) receives signals outside the normal operating parameters from the oil pressure sensor, or when actual oil pressure falls below the manufacturer's specified threshold during engine operation.

This fault is critical for the PC750-7's SAA6D140E-5 engine because inadequate oil pressure monitoring can lead to catastrophic engine damage. The oil pressure system ensures proper lubrication of critical engine components, including bearings, camshafts, and turbocharger assemblies. When E-31 activates, the machine's protection systems may engage to prevent severe mechanical failure.

Common Symptoms

When Code E-31 is active, operators typically experience:

• Warning light illumination on the instrument cluster, specifically the oil pressure warning lamp (red)
• Engine derate mode or automatic shutdown if pressure drops critically low
• Audible alarm from the cab monitoring system
• Erratic oil pressure gauge readings or gauge showing zero pressure despite engine running
• Reduced engine performance as the ECM limits power output to protect internal components

Potential Causes

The most common technical causes for E-31 on used PC750-7 excavators include:

• Failed oil pressure sensor (Komatsu part 6732-81-3140) due to internal diaphragm wear or electrical component failure
• Damaged wiring harness between the sensor and ECM, particularly at flex points near the engine mount where vibration causes wire chafing
• Corroded or loose electrical connectors at the sensor terminal, common in machines with high operating hours in wet environments
• Actual low engine oil pressure caused by worn oil pump, clogged oil filter, or excessive bearing clearances
• ECM internal fault in the oil pressure monitoring circuit (rare but possible in high-hour machines)
• Contaminated engine oil causing sensor port blockage

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection Begin by checking actual engine oil level using the dipstick. Inspect the oil pressure sensor (located on the engine block's left side) for physical damage, oil leaks, or loose mounting. Examine the wiring harness from sensor to ECM for visible damage, particularly where it passes through the engine valley and along the frame rail.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. The PC750-7 oil pressure sensor should read approximately 50-150 ohms at room temperature (consult service manual for exact specifications). Check for continuity in the wiring harness from sensor to ECM pin. Measure supply voltage at the sensor connector with ignition on—should read approximately 5 volts from the ECM.

Step 3: Mechanical Verification Install a mechanical oil pressure gauge at the sensor port to verify actual engine oil pressure. At operating temperature and idle, pressure should be minimum 50 psi (345 kPa); at rated RPM, expect 85-100 psi (586-690 kPa). If mechanical pressure is correct but code persists, replace the sensor.

Step 4: Used Equipment Considerations For used excavators, thoroughly inspect connector terminals for corrosion using electrical contact cleaner. Check harness routing for rub points against engine components—a common issue after 8,000+ hours. Verify the oil filter hasn't been bypassed due to previous maintenance shortcuts. Use Komatsu KOMTRAX or compatible diagnostic software to monitor real-time sensor values and confirm ECM functionality.

Step 5: Component Replacement Replace the oil pressure sensor with genuine Komatsu parts when possible. After replacement, clear codes using diagnostic software, run the engine through operating temperature cycles, and monitor for code recurrence.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC750-7 service manual and consider professional technician assistance for complex repairs. Improper diagnosis can lead to equipment damage or safety hazards.