Komatsu PC400-6 Fault Code E308: Complete Diagnostic Guide

What is Komatsu PC400-6 Fault Code E308?

Fault Code E308 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 SAA6D125E-3 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 safe operating parameters. When the ECM detects voltage readings outside the expected range (typically 0.5-4.5V) or actual pressure below threshold values, it triggers E308. This is critical for the PC400-6 because insufficient oil pressure can lead to bearing failure, piston seizure, and complete engine destruction—repairs that can exceed $30,000 on used machines.

Common Symptoms

When Code E308 is active, operators typically experience:

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Automatic engine derate or shutdown in severe cases, limiting machine operation to protect the engine
• Erratic oil pressure gauge readings or gauge showing abnormally low pressure (below 2.5 kg/cm² at rated RPM)
• Increased engine noise such as valve train clatter or knocking sounds indicating lubrication issues
• Intermittent code activation during cold starts or under heavy load conditions

Potential Causes

The most common technical causes for E308 on used PC400-6 excavators include:

• Failed oil pressure sensor due to internal diaphragm deterioration or contamination (common after 8,000+ hours)
• Damaged wiring harness at the sensor connector, particularly where the harness routes near the engine block and experiences heat/vibration
• Corroded or loose electrical connections at the sensor or ECM terminals, especially on machines operated in wet/coastal environments
• Actual low oil pressure caused by worn oil pump, clogged oil filter, diluted engine oil, or excessive bearing clearances
• ECM calibration issues or internal ECM faults affecting the pressure monitoring circuit

How to Troubleshoot and Fix Code E308

Step 1: Visual Inspection and Basic Checks

Begin by checking actual engine oil level and condition. Inspect the oil pressure sensor (located on the left side of the engine block) and its wiring harness for obvious damage, oil contamination, or corroded connectors. On used excavators, pay special attention to harness routing where it contacts hot engine surfaces or sharp edges.

Step 2: Electrical Testing

Using a digital multimeter, disconnect the oil pressure sensor and measure resistance across its terminals (should be 50-150 ohms at room temperature). Check supply voltage at the sensor connector with ignition on—should read approximately 5V. Inspect ground continuity between the sensor ground wire and chassis ground (less than 1 ohm resistance).

Step 3: Sensor and System Verification

Install a mechanical oil pressure gauge at the sensor port to verify actual pressure (should be 4.5-5.5 kg/cm² at rated RPM when warm). If mechanical pressure is normal but E308 persists, replace the oil pressure sensor (Komatsu part 7861-93-1650). If pressure is low, investigate oil pump condition, bearing clearances, and oil viscosity. Use Komatsu diagnostic software (KOMTRAX) to monitor live sensor data and verify ECM functionality.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC400-6 service manual and consider professional assessment, especially when dealing with critical engine protection systems on used equipment.