What is Komatsu PC55MR-2 Fault Code S-13?

Fault Code S-13 on the Komatsu PC55MR-2 excavator indicates a malfunction in the swing motor solenoid valve circuit or hydraulic swing system. This code signals that the Electronic Control Module (ECM) has detected an abnormal electrical signal or open circuit condition within the swing motor's proportional control valve system.

The swing motor is critical for the PC55MR-2's upper structure rotation capabilities. This compact excavator relies on precise hydraulic flow control through electronically-operated solenoid valves to manage swing speed and direction. When Code S-13 appears, it means the machine's control system cannot properly regulate hydraulic pressure to the swing motor, directly impacting operational efficiency and potentially causing unsafe rotation behavior during jobsite maneuvers.

Common Symptoms

When Code S-13 is active on your Komatsu PC55MR-2, operators typically experience:

• Erratic or complete loss of swing function – the upper structure may rotate inconsistently, jerk during movement, or fail to swing entirely
• Warning light illuminated on the operator display panel, often accompanied by a diagnostic trouble code readout
• Reduced swing speed or inability to achieve full rotational velocity even at maximum joystick input
• Unusual hydraulic noises such as whining or cavitation sounds from the swing motor area
• Intermittent swing operation that works occasionally but fails unpredictably during the work cycle

Potential Causes

Several technical issues commonly trigger Code S-13 on used PC55MR-2 excavators:

• Damaged wiring harness leading to the swing motor solenoid valve – particularly where the harness passes near the swing bearing or frame pivot points where rubbing occurs over time
• Failed swing motor proportional solenoid valve due to internal coil burnout or contaminated hydraulic fluid causing stuck spool valves
• Corroded or loose electrical connectors at the solenoid valve connection point, especially on machines with significant operating hours in wet or corrosive environments
• Open circuit or short to ground in the control wiring between the ECM and swing valve assembly
• ECM software glitch or internal controller fault (less common but possible in older machines)
• Low voltage supply to solenoid due to corroded ground connections or failing alternator output

How to Troubleshoot and Fix Code S-13

Step 1: Visual Inspection Begin by inspecting the wiring harness routing from the main controller to the swing motor solenoid valve. On used excavators, check specifically where the harness passes through the swing post area and near the hydraulic pump—these are known rub points on the PC55MR-2. Look for chafed insulation, pinched wires, or evidence of rodent damage.

Step 2: Electrical Testing Using a digital multimeter, disconnect the solenoid valve connector and measure resistance across the solenoid coil terminals. Typical specifications should be between 10-30 ohms (consult your service manual for exact values). Check for continuity to ground—any reading indicates a short circuit. Inspect the connector pins for corrosion or bent terminals, which are extremely common on older machines stored outdoors.

Step 3: Voltage Supply Check With the ignition key on (engine off), backprobe the connector to verify the solenoid receives proper supply voltage (typically 12-24V depending on machine configuration). If voltage is absent, trace back toward the ECM checking for broken wires or blown fuses in the control circuit.

Step 4: Solenoid Valve Function Test If electrical tests pass, the proportional solenoid valve itself may be mechanically failed. Remove the valve assembly and inspect for contamination, stuck spools, or damaged O-rings. Hydraulic contamination is particularly problematic in used equipment with inconsistent fluid maintenance history.

Step 5: ECM Diagnostics Connect Komatsu diagnostic software (KOMTRAX or compatible scan tool) to read detailed fault data and perform actuator tests. The software can command the swing solenoid directly to isolate whether the issue is controller-based or field device failure.

Critical for Used Equipment: Before replacing expensive components like the solenoid valve or ECM, thoroughly clean all electrical connections with contact cleaner and apply dielectric grease. Check the main chassis ground connections and battery terminals—poor grounds cause many false codes on aging excavators.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC55MR-2 service manual and consider professional diagnostic assistance for complex electrical or hydraulic system repairs. Improper repairs may cause equipment damage or safety hazards.