Komatsu PC750SE-7 Fault Code E-31: Complete Diagnostic Guide

What is Komatsu PC750SE-7 Fault Code E-31?

Fault Code E-31 indicates a malfunction in the engine oil pressure sensor circuit or abnormally low engine oil pressure detected by the Engine Control Module (ECM). This code specifically relates to the oil pressure monitoring system that protects the Komatsu SAA6D140E-5 engine from catastrophic damage due to inadequate lubrication.

The oil pressure sensor sends continuous voltage signals to the ECM, which monitors whether oil pressure remains within the manufacturer's specified range during operation. When pressure drops below threshold values or the sensor circuit shows electrical anomalies, the ECM triggers E-31 and may initiate protective measures. For the PC750SE-7's high-output diesel engine, maintaining proper oil pressure is absolutely critical—insufficient lubrication can destroy bearings, camshafts, and turbocharger components within minutes of operation.

Common Symptoms

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

• Warning light illumination on the monitor panel, often accompanied by audible alarms
• Engine derate or automatic shutdown in severe cases to prevent engine damage
• Erratic oil pressure gauge readings or gauge showing zero pressure despite engine running
• Reduced hydraulic performance if the operator continues working with derated engine power
• Intermittent code appearance during cold starts or high-load operations, particularly in used machines

Potential Causes

The most common technical reasons for E-31 on used PC750SE-7 excavators include:

• Failed oil pressure sensor due to age, heat cycling, or internal diaphragm deterioration
• Damaged wiring harness at known rub points near the engine block or along the frame rail
• 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 for operating conditions
• ECM calibration drift or software glitches in older control modules

How to Troubleshoot and Fix Code E-31

Step 1: Visual Inspection and Basic Checks Begin by verifying engine oil level using the dipstick—ensure oil is at the proper mark and check oil condition. Inspect the oil pressure sensor (typically located on the engine block near the oil filter housing) for physical damage, oil leaks, or loose mounting. Examine the wiring harness from sensor to ECM for chafing, cuts, or heat damage, paying special attention to areas where harnesses contact frame members.

Step 2: Electrical Testing Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across the sensor terminals (typical specification: 50-150 ohms at room temperature, but consult service manual). Check for supply voltage at the connector (should be approximately 5V reference voltage from ECM). Inspect connector pins for corrosion or bent terminals—critical on used excavators exposed to moisture and debris.

Step 3: Mechanical Verification If electrical tests pass, install a mechanical oil pressure gauge at the test port to verify actual oil pressure (should be 30-50 PSI at idle, 60-85 PSI at rated RPM for this engine). Low mechanical pressure indicates internal engine issues requiring immediate attention. For used machines, consider that previous repairs may have introduced incorrect sensors or aftermarket parts with incompatible specifications.

Step 4: Component Replacement and Validation Replace the oil pressure sensor with a genuine Komatsu part (part number specific to SAA6D140E-5 engine). Clear fault codes using Komatsu diagnostic software (KOMTRAX) or compatible scan tool. Run the engine through various load conditions while monitoring live data to confirm proper sensor operation and stable oil pressure readings.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu service manual for your specific serial number and consider professional diagnosis for complex issues, especially those involving internal engine problems.