What is Kobelco SK350LC-8 Fault Code F043?

Kobelco SK350LC-8 Fault Code F043 indicates a malfunction in the engine pre-heating (glow plug) system circuit. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormal voltage, current draw, or resistance in the glow plug relay circuit or associated wiring harness.

The glow plug system is critical for reliable cold-start performance on the Isuzu 6WG1X diesel engine powering the SK350LC-8. When this code activates, the ECM registers that the pre-combustion heating system cannot function properly, which compromises starting ability in low ambient temperatures. On used excavators, this fault frequently stems from deteriorated electrical connections or relay failures rather than the glow plugs themselves. Addressing F043 promptly prevents extended cranking cycles that drain batteries and stress the starter motor.

Common Symptoms

• Hard starting or no-start condition, especially in cold weather (below 40°F/4°C)
• Check Engine light illuminated on the instrument cluster
• Extended cranking time before the engine fires, with excessive white smoke during initial startup
• Glow plug indicator light may flash or fail to illuminate during the pre-heat cycle
• Rough idle immediately after cold start until engine reaches operating temperature

Potential Causes

The most common technical causes for F043 on used SK350LC-8 excavators include:

• Faulty glow plug relay (located in the engine compartment fuse/relay box) – internal contacts wear over time
• Damaged wiring harness between the ECM and glow plug relay, particularly where the harness routes near the engine mount (known rubbing point)
• Corroded or loose electrical connectors at the relay socket or ECM pins C43/C44
• Failed individual glow plugs creating excessive current draw that trips ECM protection
• Low battery voltage during pre-heat cycle (below 22V on this 24V system)
• ECM software calibration issue or internal ECM fault (rare, but possible on high-hour machines)

How to Troubleshoot and Fix Code F043

Step 1: Visual Inspection Begin by inspecting the glow plug relay and all associated wiring. On used excavators, check the main engine harness where it passes over the left engine mount – this is a common wear point. Look for chafed insulation, corroded pins, or heat damage on connectors. Clean all terminals with electrical contact cleaner.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage exceeds 24V with the engine off. Locate the glow plug relay (typically in the right-side fuse box) and check for 12V supply voltage at terminal 30 (constant power). With the key in the "ON" position during pre-heat, verify the ECM signal at relay terminal 85 (should read 12V during glow cycle).

Step 3: Component Testing Test glow plug relay operation by bridging terminals 30 and 87 – you should hear the relay click. Measure current draw during the glow cycle; normal draw is approximately 40-60 amps for all six cylinders. Excessive current (above 80 amps) indicates a failed glow plug. If relay and wiring test good, use Kobelco INSITE diagnostic software to monitor individual glow plug activation and confirm ECM functionality.

Step 4: Repair and Verification Replace faulty components (relay is most common). On used machines, consider replacing the entire relay-to-ECM harness if insulation shows age-related cracking. After repairs, clear codes using diagnostic software and perform three cold-start cycles to verify the fix.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Kobelco service manual and consider professional diagnostic assistance for complex electrical issues, especially on used equipment with unknown maintenance history.