Komatsu PC50MR-2 Fault Code S-5: Complete Diagnostic Guide

What is Komatsu PC50MR-2 Fault Code S-5?

Fault Code S-5 on the Komatsu PC50MR-2 indicates a malfunction in the swing motor solenoid circuit or swing motor control system. This code is triggered when the Electronic Control Module (ECM) detects abnormal voltage, resistance, or signal disruption in the electrical circuit controlling the swing motor's hydraulic solenoid valve.

The swing motor system is critical for the PC50MR-2's upper structure rotation. This compact excavator relies on precise hydraulic pressure modulation controlled by electronic solenoids to execute smooth, operator-commanded swing movements. When the ECM cannot properly energize or communicate with the swing solenoid, it logs S-5 to prevent erratic machine behavior and potential hydraulic system damage.

Common Symptoms

Operators experiencing fault code S-5 may notice:

• Sluggish or completely unresponsive swing function despite normal hydraulic pump operation
• Intermittent swing jerking or sudden stopping during rotation cycles
• Warning indicator illuminated on the instrument panel (specific to PC50MR-2 dash configuration)
• Swing function works intermittently when controls are manipulated multiple times
• No audible solenoid "click" when swing joystick is activated (detectable near swing motor assembly)

Potential Causes

The most common technical failures triggering S-5 on used PC50MR-2 excavators include:

• Swing motor solenoid coil failure due to internal winding breakdown (common after 4,000+ operating hours)
• Harness connector corrosion at the swing motor plug connection, especially on machines operated in wet/marine environments
• Wiring harness chafing where cables route along the swing bearing—a known wear point on this model
• ECM internal driver circuit fault (less common but possible in high-hour machines)
• Low battery voltage causing insufficient solenoid energization (below 11.5V DC)
• Contaminated hydraulic oil causing solenoid valve spool sticking

How to Troubleshoot and Fix Code S-5

Step 1: Visual Inspection
Disconnect the battery. Inspect the swing motor solenoid connector for bent pins, moisture intrusion, or corrosion (white/green deposits). Check the entire harness routing from the ECM to the swing motor for abrasion points where cables contact the swing bearing housing.

Step 2: Electrical Testing
Using a digital multimeter, measure solenoid coil resistance at the disconnected solenoid plug. Specification is typically 10-15 ohms (consult PC50MR-2 service manual for exact values). Test supply voltage from the ECM side—should read battery voltage (12V) when swing function is commanded.

Step 3: Circuit Continuity Check
Verify wiring continuity from ECM connector pin (reference wiring diagram) to solenoid. Check for short circuits to ground using the multimeter's ohm setting. On used excavators, deteriorated wire insulation often creates intermittent ground faults.

Step 4: Component Replacement
If resistance/voltage tests fail, replace the swing motor solenoid valve. Before reinstalling, apply dielectric grease to connector terminals. For harness damage, repair using OEM-spec 16-gauge wire and heat-shrink connectors—not electrical tape, which degrades in hydraulic fluid exposure.

Step 5: System Reset and Verification
Clear fault codes using Komatsu diagnostic software (KOMTRAX) or by battery disconnect (30 seconds). Test swing operation through full 360-degree rotation under load.

---

Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu PC50MR-2 service manual and consider professional technician assistance for complex electrical diagnostics or hydraulic system repairs.