What is Kobelco SK130-8 Fault Code 6631?

Fault Code 6631 on the Kobelco SK130-8 excavator indicates a malfunction in the engine oil pressure sensor circuit or an abnormal oil pressure reading detected by the ECM (Engine Control Module). This diagnostic trouble code (DTC) specifically points to either an electrical issue within the sensor wiring harness, a failing oil pressure sensor, or an actual mechanical oil pressure problem in the engine's lubrication system.

The oil pressure sensor on the SK130-8's Hino engine is critical for monitoring lubrication health and preventing catastrophic engine damage. When the ECM detects voltage signals outside the normal range (typically 0.5-4.5V) or oil pressure readings that don't correlate with engine RPM, it triggers Code 6631. For used excavators, this fault can indicate sensor deterioration, wiring damage from years of vibration, or legitimate oil system wear requiring immediate attention.

Common Symptoms

When Code 6631 is active on your SK130-8, you may experience:

• Check Engine Light illuminated on the instrument cluster with audible warning alarm
• Engine derate mode or reduced power output as a protective measure
• Oil pressure gauge reading abnormally low, high, or erratic on the display
• Engine shutdown in severe cases if critical oil pressure thresholds aren't met
• Intermittent warning that comes and goes with engine temperature changes or machine vibration

Potential Causes

The most common technical reasons for Code 6631 appearing on used SK130-8 excavators include:

• Failed oil pressure sensor due to internal component degradation (common after 5,000+ hours)
• Damaged wiring harness or corroded connectors, particularly at the sensor mounting point where engine heat and vibration cause wear
• Low engine oil level or contaminated oil affecting actual pressure readings
• Worn oil pump or clogged oil passages reducing system pressure (mechanical issue)
• ECM voltage supply issues providing incorrect reference voltage to the sensor circuit
• Shorted or open circuits in the sensor signal wire from rubbing against engine components

How to Troubleshoot and Fix Code 6631

Step 1: Visual Inspection and Oil Level Check Begin by verifying the engine oil level using the dipstick and inspecting oil condition for contamination or metal particles. Check the oil pressure sensor connector (typically located on the engine block near the oil filter) for corrosion, bent pins, or moisture intrusion—common issues on used machines exposed to harsh environments.

Step 2: Electrical Circuit Testing Using a digital multimeter, disconnect the oil pressure sensor and measure resistance across the sensor terminals (refer to Kobelco service manual for specific values, typically 50-200 ohms at ambient temperature). Test the supply voltage at the harness connector with ignition on; it should read approximately 5V. Check for continuity between the sensor ground and chassis ground. On used excavators, inspect the entire wiring harness for rubbing points where insulation may be worn through, especially near engine mounts.

Step 3: Sensor Replacement and Verification If electrical tests pass but the code persists, install a genuine Kobelco/Hino oil pressure sensor (part-specific to SK130-8). After replacement, clear the fault code using diagnostic software (Kobelco Dr.EX or compatible scan tool) and monitor oil pressure readings at idle and high RPM. If pressure remains abnormal with a new sensor, investigate mechanical oil system issues including oil pump performance and bearing clearances—critical checks for high-hour used machines.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific machine's serial number range and consider professional diagnostic assistance for complex electrical or mechanical issues, especially on used equipment with unknown maintenance history.