Komatsu PC35MR-2 Fault Code S-14: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code S-14?

Fault Code S-14 on the Komatsu PC35MR-2 indicates a malfunction in the swing motor lock solenoid circuit. This code specifically signals that the Electronic Control Module (ECM) has detected an abnormal electrical condition—either an open circuit, short circuit, or excessive resistance—in the wiring or solenoid that controls the swing lock mechanism.

The swing lock solenoid is critical for this compact excavator's operational safety. It electrically controls the hydraulic valve that engages and disengages the swing brake, allowing or preventing the upper structure from rotating. When this system fails, the machine may experience unwanted swing movement during transport or unintended lockup during operation, creating serious safety hazards on job sites.

Common Symptoms

When Code S-14 is active on your PC35MR-2, operators typically experience:

• Swing function completely disabled or intermittently locking during rotation
• Warning light illuminated on the instrument panel with error code display
• Swing brake fails to release when starting operations, preventing upper structure rotation
• Abnormal hydraulic sounds (chattering or whining) from the swing motor area
• Machine enters reduced performance mode, limiting other hydraulic functions as a safety precaution

Potential Causes

The most common technical failures triggering S-14 on used PC35MR-2 excavators include:

• Swing lock solenoid coil failure due to age-related insulation breakdown or moisture infiltration
• Damaged wiring harness near the swing motor mounting area where cables experience constant flexing and vibration
• Corroded or loose connector pins at the solenoid plug—a frequent issue on machines operating in wet or marine environments
• Worn harness grommets allowing wire chafing against the swing bearing housing (known wear point on this model)
• ECM internal circuit degradation affecting solenoid driver output (less common but possible on high-hour machines)
• Voltage drop issues from deteriorated main power supply connections or failing alternator

How to Troubleshoot and Fix Code S-14

Step 1: Visual Inspection Locate the swing lock solenoid mounted on the swing motor assembly. Inspect the wiring harness from the solenoid back to the main chassis connector for visible damage, abrasion, or pinch points. Pay special attention to where the harness passes through the swing bearing area—this is a known rub point on used PC35MR-2 machines. Check the solenoid connector for corrosion, moisture, or bent pins.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid connector and measure coil resistance across the solenoid terminals. Komatsu specifications typically call for 20-30 ohms (verify with your service manual). An open circuit (infinite resistance) indicates coil failure. Next, check for supply voltage at the harness connector with the ignition on—you should see approximately 12 volts.

Step 3: Circuit and Ground Testing Test for continuity between the solenoid ground wire and chassis ground. High resistance (above 1 ohm) suggests a poor ground connection. Inspect the ECM connector pins (specifically the solenoid driver circuit) for corrosion or backing out. On used excavators, connector terminal tension often degrades, causing intermittent faults.

Step 4: Component Replacement If resistance is out of specification, replace the swing lock solenoid (Komatsu part number should be verified through your dealer). If wiring shows damage, repair using marine-grade heat shrink connectors and re-route away from pinch points. After repairs, clear the code using Komatsu diagnostic software (KOMTRAX or aftermarket tools like Jpro) and cycle the swing function multiple times to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information for experienced technicians. Always consult the official Komatsu PC35MR-2 service manual for torque specifications, exact resistance values, and safety procedures. If unfamiliar with hydraulic or electrical systems, contact a certified Komatsu technician to prevent injury or further machine damage.