Komatsu PC450-6 Fault Code E308: Complete Diagnostic Guide

What is Komatsu PC450-6 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 minimum thresholds (usually below 50 kPa at idle), it triggers E308. This protection system is critical because the PC450-6's high-output engine operates under extreme loads, and even brief periods of low oil pressure can cause bearing failure, piston seizure, or complete engine destruction.

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
• Increased engine noise (knocking or ticking) if actual oil pressure is genuinely low
• Intermittent code activation during cold starts or high-load operations on used machines

Potential Causes

The most common technical causes for E308 on used PC450-6 excavators include:

• Failed oil pressure sensor (common failure point after 8,000+ hours due to heat cycling and vibration)
• Damaged or corroded wiring harness between the sensor and ECM, particularly at connector C-103 near the engine block
• Low engine oil level or use of incorrect viscosity oil for operating conditions
• Worn oil pump or clogged oil pickup screen reducing actual system pressure
• Faulty ECM (rare, but possible in high-hour machines with moisture intrusion)
• Blocked oil passages or sludge buildup in engines with poor maintenance history

How to Troubleshoot and Fix Code E308

Step 1: Visual Inspection and Oil Level Verification Check engine oil level using the dipstick—ensure oil is at the proper level and appears clean. Inspect the oil pressure sensor (located on the left side of the engine block near the oil filter) for physical damage, oil leaks, or corroded connectors. Examine the wiring harness for chafing, particularly where it routes near the engine mount and hydraulic lines.

Step 2: Electrical Testing with Diagnostic Tools Using a digital multimeter, disconnect the oil pressure sensor connector and measure resistance across the sensor terminals. Specifications typically range from 50-150 ohms at room temperature. Check supply voltage at the harness connector—should read approximately 5V with ignition on. Test harness continuity between the sensor connector and ECM pin B-27 for opens or shorts to ground.

Step 3: Sensor Replacement and System Verification If electrical tests indicate sensor failure (common on used excavators), replace with a genuine Komatsu sensor (Part #6732-81-3140). For used machines, always apply dielectric grease to connector pins before reassembly to prevent future corrosion. Clear codes using Komatsu diagnostic software (KOMTRAX) or a compatible scan tool, then monitor oil pressure during a 20-minute test run under varying loads.

Step 4: Mechanical System Inspection If the code persists after sensor replacement, verify actual oil pressure using a mechanical pressure gauge installed at the sensor port. Pressure should read 300-450 kPa at rated RPM. Low readings indicate worn oil pump, clogged oil filter, or internal engine wear requiring professional teardown.

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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 consider professional assistance for complex repairs, especially on used equipment with unknown maintenance history.