Komatsu PC55MR-2 Fault Code S-14: Technical Guide

What is Komatsu PC55MR-2 Fault Code S-14?

Fault Code S-14 indicates a malfunction in the engine preheating system, specifically the glow plug circuit or relay failure. This code triggers when the Engine Control Module (ECM) detects abnormal resistance, open circuit, or short circuit conditions in the glow plug system during cold start operations.

On the Komatsu PC55MR-2 mini excavator, the glow plug system is critical for reliable diesel engine starting, especially in cold weather conditions. The preheating circuit ensures proper combustion chamber temperature before cranking, and system failures can lead to hard starting or complete no-start situations that significantly impact jobsite productivity.

Common Symptoms

When Code S-14 is active on your PC55MR-2, you may experience:

• Extended cranking time or engine failing to start in cold conditions (below 40°F/5°C)
• Glow plug indicator light remaining illuminated or flashing abnormally on the instrument panel
• White or gray exhaust smoke during cold starts due to incomplete combustion
• Engine running rough for the first few minutes after cold start
• Intermittent starting issues that worsen as ambient temperatures drop

Potential Causes

The most common technical causes for S-14 on used PC55MR-2 excavators include:

• Failed glow plug relay or timer unit (high-failure component on older machines)
• One or more burned-out glow plugs creating abnormal circuit resistance
• Corroded or damaged wiring harness connections at the glow plug connector—common wear point due to engine vibration
• Faulty ECM glow plug driver circuit (less common but possible on high-hour machines)
• Broken or frayed wiring near the engine block where harness rubs against frame components
• Low battery voltage causing insufficient current flow to activate glow plugs properly

How to Troubleshoot and Fix Code S-14

Step 1: Visual Inspection Check all glow plug wiring harnesses for visible damage, particularly where they route along the valve cover. Inspect connector pins for corrosion or bent terminals. On used excavators, harness chafing against the engine block is extremely common.

Step 2: Test Glow Plug Resistance Using a digital multimeter, disconnect each glow plug and measure resistance. Specification is typically 0.5-2.0 ohms per plug. Readings above 5 ohms or infinite resistance indicate failed plugs requiring replacement.

Step 3: Check Relay Operation Locate the glow plug relay in the fuse box. With ignition on, listen for relay click and measure voltage at relay output terminal—should read battery voltage (12V) when activated. Replace relay if no voltage present.

Step 4: Verify Power Supply Test battery voltage under load during glow plug activation. Voltage drop below 11V indicates weak battery or poor ground connections affecting glow plug performance.

Step 5: Clear Code and Test After repairs, clear fault codes using Komatsu diagnostic software or by disconnecting battery for 30 seconds. Perform cold start test to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information. For complex electrical diagnostics or if you're unfamiliar with high-current circuits, consult a certified Komatsu technician or qualified heavy equipment mechanic to prevent damage or injury.