Komatsu PC750LC-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC750LC-7 Fault Code E-31?

Fault Code E-31 on the Komatsu PC750LC-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 PC750LC-7's SAA6D140E-3 engine because inadequate oil pressure can lead to catastrophic bearing failure, turbocharger damage, and complete engine seizure. The ECM monitors oil pressure continuously to protect internal components from insufficient lubrication, making this code a high-priority diagnostic concern.

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)
• Audible alarm sounding from the cab, indicating critical engine condition
• Engine derate or automatic shutdown in severe cases to prevent damage
• Reduced hydraulic performance as the ECM limits engine RPM
• Fluctuating oil pressure gauge readings or gauge showing abnormally low pressure

Potential Causes

The most common technical causes for E-31 on used PC750LC-7 excavators include:

• Failed oil pressure sensor due to internal diaphragm deterioration or contamination
• Damaged wiring harness between the sensor and ECM, particularly at known rub points near the engine mount brackets
• Corroded or loose electrical connectors at the sensor or ECM interface
• Actual low oil pressure caused by worn oil pump, clogged oil filter, or bearing clearance issues
• Low engine oil level or use of incorrect viscosity oil
• ECM calibration issues or internal ECM fault (less common)

How to Troubleshoot and Fix Code E-31

Step 1: Initial Visual Inspection Check engine oil level using the dipstick and verify correct SAE 15W-40 or manufacturer-specified oil is used. Inspect the oil pressure sensor location (typically on the main oil gallery near the oil filter housing) for obvious damage, oil leaks, or loose connections.

Step 2: Electrical Circuit Testing Using a digital multimeter, check the oil pressure sensor connector for corrosion or bent pins. With the ignition on but engine off, measure voltage supply to the sensor (should be approximately 5V reference voltage). Check ground continuity and inspect the wiring harness along its entire length, especially where it passes near moving components or sharp edges—common wear points on used machines.

Step 3: Sensor Verification Remove the oil pressure sensor and inspect the threads for metal debris or sealant contamination. Using a mechanical oil pressure gauge, verify actual oil pressure at idle (should be 50-70 psi minimum) and at rated RPM (100-120 psi typical). If mechanical pressure is correct but the code persists, replace the oil pressure sensor (Komatsu part number 6732-81-3140 or equivalent).

Step 4: Advanced Diagnostics Connect Komatsu diagnostic software (KOMTRAX Plus) to read live sensor data and compare actual versus reported pressure values. For used excavators with high hours, inspect the oil pump drive gear and consider an oil analysis to check for bearing material, indicating internal wear requiring major service.

Critical Note for Used Equipment: Before replacing components, thoroughly clean all electrical connectors with contact cleaner and apply dielectric grease. Check for harness chafing against the frame—a common issue after 8,000+ operating hours.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific machine serial number and seek qualified diesel technician assistance for complex repairs involving engine internals or ECM programming.