What is Kobelco SK135SRLC-2 Fault Code P0266 (659-8)?

Fault Code P0266 on the Kobelco SK135SRLC-2 indicates a malfunction in the Cylinder #2 Contribution/Balance circuit. This diagnostic trouble code (DTC) specifically points to an issue where the Engine Control Module (ECM) has detected that cylinder #2 is not contributing properly to overall engine power output, creating an imbalance in combustion efficiency.

In Kobelco's Isuzu-based diesel engines, this code triggers when the ECM monitors fuel injection timing and quantity for each cylinder and finds that cylinder #2's performance deviates significantly from expected parameters. This directly affects the SK135SRLC-2's fuel efficiency, power delivery, and emissions compliance. Left unaddressed, this imbalance can lead to increased exhaust temperatures, reduced hydraulic performance, and accelerated engine wear on the affected cylinder.

Common Symptoms

• Engine rough idling or noticeable vibration at low RPM, particularly when the machine is warming up
• Loss of hydraulic power during digging or lifting operations, as the engine struggles to maintain consistent power output
• Black or gray exhaust smoke indicating incomplete combustion from the affected cylinder
• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument panel
• Increased fuel consumption without corresponding increase in work performance

Potential Causes

The most common technical causes for P0266 on used SK135SRLC-2 excavators include:

• Faulty fuel injector #2 – wear, carbon buildup, or internal failure preventing proper fuel atomization
• Injector wiring harness damage – corrosion, rubbing, or connector pin issues at cylinder #2's injector connector (common at harness routing near engine block)
• Low fuel pressure affecting cylinder #2 specifically due to clogged fuel filter or failing high-pressure fuel pump
• ECM internal fault – rare but possible in high-hour machines where the ECM's injector driver circuit has degraded
• Compression loss in cylinder #2 from worn piston rings, valve issues, or head gasket failure
• Injector calibration data corruption within the ECM memory

How to Troubleshoot and Fix Code P0266 (659-8)

Step 1: Visual Inspection and Basic Checks Begin by inspecting the fuel injector harness at cylinder #2. On used excavators, check for wire chafing where the harness passes near the engine's valve cover and exhaust manifold. Examine the injector connector for corrosion, moisture intrusion, or bent pins. Clean all connections with electrical contact cleaner.

Step 2: Injector Resistance and Circuit Testing Using a digital multimeter, disconnect the injector connector and measure resistance across the injector solenoid terminals. Compare readings to manufacturer specifications (typically 0.4-0.8 ohms for Isuzu injectors). Check for voltage supply at the harness connector with ignition on – you should see battery voltage on the power wire. Test for continuity between the ECM and injector connector to rule out open circuits.

Step 3: Fuel System and Compression Verification Perform a cylinder compression test on cylinder #2 and compare to other cylinders (should be within 10% variance). Check fuel rail pressure with a diagnostic pressure gauge during cranking and operation. If available, use Kobelco diagnostic software to perform an injector balance test, which commands each injector individually to identify performance discrepancies.

Step 4: Component Replacement and Validation If testing confirms injector failure, replace the cylinder #2 fuel injector with OEM or quality aftermarket parts, ensuring proper torque specifications and new copper sealing washers. For used excavators with 5,000+ hours, consider replacing all injector o-rings and seals as preventive maintenance. Clear the fault code, perform a complete ECM relearn procedure, and monitor for code recurrence during a 30-minute operational test.

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Disclaimer: This guide provides general diagnostic information. Always consult the Kobelco service manual specific to your machine's serial number and seek professional diesel technician assistance for complex fuel system repairs requiring specialized tools or calibration equipment.