Komatsu PC35MR-2 Fault Code S-11: Complete Diagnostic Guide

What is Komatsu PC35MR-2 Fault Code S-11?

Fault Code S-11 on the Komatsu PC35MR-2 indicates a malfunction in the swing motor circuit, specifically related to the swing brake solenoid valve electrical system. This code triggers when the ECM (Engine Control Module) detects an abnormal voltage or current draw in the swing brake control circuit.

The swing brake solenoid controls hydraulic pressure that releases the swing motor brake, allowing the upper structure to rotate. When this circuit fails, the ECM cannot properly command brake release, directly impacting the machine's ability to perform slewing operations safely. On compact excavators like the PC35MR-2, this system is critical for precision work in confined spaces where accurate swing control is essential.

Common Symptoms

When fault code S-11 is active, operators typically experience:

• Swing function completely disabled or intermittently non-responsive when attempting to rotate the upper structure
• Swing brake remains engaged even when joystick controls are activated
• Warning light illuminated on the instrument panel (typically a wrench or diagnostic icon)
• Jerky or delayed swing movement before complete function loss
• Audible clicking from the solenoid valve area without corresponding hydraulic action

Potential Causes

The most common technical causes for code S-11 on used PC35MR-2 excavators include:

• Swing brake solenoid coil failure due to internal short circuit or open winding (resistance typically should read 20-30 ohms)
• Damaged wiring harness near the swing motor mounting area where cable flexing during rotation causes wire breakage or insulation wear
• Corroded or loose connector pins at the solenoid valve plug, especially common in machines with water exposure history
• ECM output driver failure in the swing brake control circuit (less common but possible in high-hour machines)
• Voltage supply issues from the main power harness, including blown fuses or faulty relays
• Contaminated connector terminals from hydraulic oil mist accumulation in the swing motor compartment

How to Troubleshoot and Fix Code S-11

Step 1: Visual Inspection Begin by accessing the swing motor assembly located beneath the operator platform. Inspect the swing brake solenoid valve and its electrical connector for obvious damage, corrosion, or oil contamination. On used excavators, check for harness chafing against the swing motor housing or frame edges—a known wear point on this model.

Step 2: Electrical Testing Disconnect the solenoid connector and use a digital multimeter to measure coil resistance across the solenoid terminals. You should read approximately 20-30 ohms at room temperature. An open circuit (infinite resistance) or very low resistance (under 5 ohms) indicates coil failure. Next, check for supply voltage at the harness connector with ignition on—you should see battery voltage (12V).

Step 3: Harness Continuity Check Trace the wiring from the solenoid back to the main machine harness connector near the engine compartment. Check for continuity and look specifically for worn insulation where the harness passes through the swing bearing area. Use Komatsu diagnostic software (KOMTRAX or dealer diagnostic tools) to command the solenoid on/off while monitoring current draw—normal operation draws 0.5-1.0 amps.

Step 4: Component Replacement If the solenoid tests faulty, replace it with a genuine Komatsu swing brake solenoid valve (part number should match original equipment). Before installation on used machines, clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Secure any loose harness sections with new zip ties, ensuring cables cannot contact moving parts.

Step 5: Clear Code and Verify After repairs, clear the fault code using diagnostic software or by disconnecting the battery for 30 seconds. Cycle the swing function multiple times in both directions while monitoring for code reoccurrence.

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Disclaimer: This guide provides general diagnostic information for Komatsu PC35MR-2 fault code S-11. Hydraulic and electrical system repairs should be performed by qualified technicians with proper training and tools. Always consult the official Komatsu service manual for your machine's serial number and follow manufacturer specifications. Improper diagnosis or repair may result in equipment damage or personal injury.