What is Kobelco SK350LC-8 Fault Code A255?

Fault Code A255 on the Kobelco SK350LC-8 excavator indicates a malfunction in the Engine Speed Sensor (Crankshaft Position Sensor) circuit. This diagnostic trouble code is triggered when the Engine Control Module (ECM) detects an abnormal signal, intermittent communication, or complete signal loss from the crankshaft position sensor.

The crankshaft position sensor plays a critical role in the Kobelco SK350LC-8's Hino J05E engine management system by monitoring engine RPM and crankshaft positioning. The ECM relies on this data to precisely control fuel injection timing, ignition sequencing, and overall engine performance. When Code A255 appears, the ECM cannot accurately determine engine speed or position, which can lead to severe operational issues or complete engine shutdown. For used excavators, this code often signals sensor degradation, wiring harness damage from environmental exposure, or connector corrosion—all common issues in older machines with accumulated operating hours.

Common Symptoms

When Code A255 is active on your SK350LC-8, operators typically experience:

• Engine fails to start or experiences extended cranking before starting
• Sudden engine stalling during operation, particularly during idle or low-load conditions
• Erratic or fluctuating engine RPM that doesn't respond consistently to throttle input
• Dashboard warning lights illuminated, specifically the engine malfunction indicator
• Loss of engine power or activation of derate mode limiting machine performance

Potential Causes

Several technical factors can trigger Code A255, especially in used excavators:

• Faulty crankshaft position sensor due to internal component failure or heat degradation
• Damaged or corroded wiring harness connections between the sensor and ECM (common wear point near engine mounts)
• Broken or frayed sensor wiring caused by vibration, rubbing against engine components, or improper previous repairs
• Contaminated or damaged sensor connector terminals from moisture intrusion, oil leakage, or dirt accumulation
• ECM internal fault or corrupted software (less common, but possible in high-hour machines)
• Incorrect sensor air gap caused by mounting bolt looseness or sensor position shift

How to Troubleshoot and Fix Code A255

Step 1: Visual Inspection Begin by locating the crankshaft position sensor on the Hino J05E engine (typically mounted near the flywheel/crankshaft pulley area). Thoroughly inspect the sensor body, mounting bracket, and wiring harness for obvious damage, oil contamination, loose connections, or physical contact with moving components. On used excavators, check for harness abrasion at known rub points where the harness routes along the engine block.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure resistance across the sensor terminals. Compare readings against Kobelco specifications (typically 200-300 ohms for inductive sensors). Check for voltage supply at the harness connector with ignition on—you should see battery voltage on the supply wire. Inspect connector pins for corrosion, bent terminals, or moisture. Test harness continuity from sensor to ECM connector.

Step 3: Sensor Gap and Replacement Verify the sensor's air gap distance to the reluctor ring using feeler gauges (specification typically 0.5-1.2mm). If electrical tests pass but symptoms persist, replace the crankshaft position sensor with a genuine Kobelco/Hino part. After installation, clear codes using Kobelco diagnostic software (Dr.EX) or a compatible scan tool, then perform a test run to verify repair.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual for your specific serial number and consider professional diagnostic assistance for complex electrical issues.