What is Komatsu PC50MR-2 Fault Code S-13?

Fault Code S-13 on the Komatsu PC50MR-2 indicates a malfunction in the swing motor lock solenoid circuit. This code triggers when the Electronic Control Module (ECM) detects an abnormal voltage reading, open circuit, or short circuit in the electrical system controlling the swing lock solenoid valve.

The swing motor lock solenoid is critical for controlling the upper structure's rotation during operation and transport. When this circuit fails, the ECM may prevent swing operation entirely to protect the hydraulic system from damage. For compact excavators like the PC50MR-2 operating in tight spaces, swing functionality is essential for productivity, making this fault code a priority repair issue.

Common Symptoms

• Swing lock warning light illuminated on the instrument panel or monitor display
• Complete loss of swing function – upper structure will not rotate in either direction
• Intermittent swing operation where the machine randomly locks during rotation
• Error beep codes or audible alarms from the operator cab upon startup
• Machine enters limp mode, restricting swing speed or other hydraulic functions

Potential Causes

The S-13 code typically results from electrical rather than mechanical failures in used machines:

• Damaged wiring harness between the ECM and swing lock solenoid, particularly where the harness passes through the center joint (common wear point on used PC50MR-2 models)
• Corroded or loose connector pins at the solenoid valve or ECM connections due to moisture intrusion
• Failed swing lock solenoid coil internally shorted or open (resistance outside 20-30 ohm specification range)
• Blown fuse or damaged relay in the solenoid power supply circuit
• ECM internal fault (less common but possible in machines with 5,000+ operating hours)

How to Troubleshoot and Fix Code S-13

Step 1: Visual Inspection Begin by inspecting the wiring harness from the swing motor base to the ECM compartment. Look for abraded insulation, pinched wires at the center joint swivel, or damaged connectors. On used excavators, pay special attention to harness routing near rotating components where friction damage occurs over time.

Step 2: Electrical Testing Using a digital multimeter, disconnect the swing lock solenoid connector and measure coil resistance across the solenoid terminals (should read 20-30 ohms). Then check for voltage supply at the connector with ignition on (should read 12-14V). Test for continuity through the entire harness back to the ECM.

Step 3: Component Testing and Replacement If resistance or voltage readings fall outside specifications, identify whether the solenoid coil or harness is faulty. Clean all connector contacts with electrical contact cleaner and apply dielectric grease. Replace the swing lock solenoid valve if the coil tests bad, or repair/replace damaged harness sections. Clear the fault code using Komatsu diagnostic software (KOMTRAX) and test swing operation.

Disclaimer: This guide provides general troubleshooting procedures. Always consult the Komatsu PC50MR-2 service manual and consider professional diagnostic assistance for complex electrical issues, especially when working with the ECM or hydraulic systems.