What is Komatsu PC120-6 Fault Code E-8?

Komatsu PC120-6 Fault Code E-8 indicates an abnormal signal from the engine oil pressure sensor circuit. This diagnostic trouble code is triggered when the Electronic Control Module (ECM) detects voltage levels outside the normal operating range from the oil pressure sensor, typically between 0.5-4.5 volts.

This fault is critical for the PC120-6 because the engine oil pressure sensor provides real-time data that prevents catastrophic engine damage. When E-8 appears, the ECM cannot accurately monitor lubrication system health, potentially leading to engine seizure if actual low oil pressure conditions exist but go undetected. The Komatsu SAA4D102E engine in this model relies heavily on precise sensor feedback for protective shutdown protocols.

Common Symptoms

• Continuous warning buzzer sounding from the operator's cab, even when engine oil pressure appears normal
• Oil pressure warning lamp illuminated on the instrument cluster (red oil can icon)
• Engine power derate or refusal to reach full throttle as a protective measure
• Intermittent code appearance that becomes more frequent during machine warm-up or under load
• Monitor panel displaying error message alongside fault code

Potential Causes

The E-8 code on used PC120-6 excavators typically stems from age-related deterioration:

• Oil pressure sensor failure due to internal diaphragm wear or contamination from metal particles in aged oil
• Wiring harness damage at known rub points near the engine mount brackets where vibration causes insulation breakdown
• Corroded connector terminals at the three-pin sensor plug, especially on machines operating in coastal or high-humidity environments
• ECM voltage supply issues providing incorrect reference voltage (typically should be 5V)
• Damaged sensor threads causing oil leakage and intermittent electrical contact
• Aftermarket sensor incompatibility if previous owner installed non-OEM replacement parts

How to Troubleshoot and Fix Code E-8

Step 1: Visual Inspection Locate the oil pressure sensor on the engine block's left side near the oil filter housing. Check for obvious oil leaks around threads, damaged wiring, or corroded connector pins. On used excavators, inspect the entire harness route for wear marks where cables contact metal surfaces.

Step 2: Electrical Testing Disconnect the sensor connector and use a multimeter to measure resistance across sensor terminals. Specification should read 50-150 ohms at room temperature. Then check harness continuity from connector to ECM pin—resistance should be less than 5 ohms. Measure supply voltage at the harness connector with ignition on: should read 4.8-5.2V.

Step 3: Signal Verification With sensor reconnected and engine running, backprobe the signal wire using a multimeter set to DC voltage. Normal reading should fluctuate between 1.5-3.5V depending on engine RPM. Static readings near 0V or 5V confirm sensor failure.

Step 4: Component Replacement If electrical tests confirm sensor fault, replace with genuine Komatsu part number 7861-93-1650. Apply anti-seize compound to threads and torque to 15-18 ft-lbs. For harness damage, repair with marine-grade heat shrink connectors rather than tape. Clear codes using Komatsu diagnostic software or disconnect battery for 30 minutes.

Disclaimer: This guide provides general diagnostic information. Always consult factory service manuals and consider professional diagnosis for complex electrical issues or if unfamiliar with high-voltage systems.