What is Komatsu PC100-6 Fault Code S-5?

Fault Code S-5 on the Komatsu PC100-6 excavator indicates a main pump solenoid valve circuit malfunction, specifically detecting an abnormal electrical signal in the hydraulic pump control system. This code triggers when the engine control module (ECM) identifies irregular current flow, open circuits, or short circuits within the main pump solenoid valve wiring harness or the solenoid itself.

The main pump solenoid valve controls hydraulic oil flow and pressure regulation, directly impacting the excavator's operational efficiency. This system is critical for the PC100-6's load-sensing hydraulic circuit, which automatically adjusts pump output based on operational demands. When this code activates, the machine may enter a protective derated mode to prevent further damage to the hydraulic system or engine components.

Common Symptoms

• Hydraulic power loss or noticeably reduced digging force across all functions (boom, arm, bucket)
• Warning light activation on the instrument panel, often accompanied by intermittent buzzer alerts
• Erratic hydraulic response where certain functions work normally while others respond sluggishly
• Engine RPM fluctuations under load, particularly during simultaneous multi-function operations
• Complete hydraulic system shutdown in severe cases, though engine continues running

Potential Causes

The S-5 code typically originates from electrical circuit failures rather than mechanical pump issues. Wiring harness damage is extremely common on used PC100-6 models, particularly where the harness routes near the swing motor or along the boom cylinder—known rub points on this model. Connector corrosion at the solenoid valve plug is prevalent in machines operating in wet or coastal environments.

Solenoid valve coil failure occurs from prolonged heat exposure or electrical spikes. The solenoid valve itself may develop internal shorts due to contamination or coil degradation. Less frequently, ECM relay failures or damaged ECM pin connections can generate false S-5 codes.

How to Troubleshoot and Fix Code S-5

Step 1: Visual Inspection
Disconnect the battery and thoroughly examine the main pump solenoid valve connector (located on the pump housing). Check for bent pins, moisture intrusion, or green corrosion deposits. Inspect the wiring harness for abrasion damage, particularly where it contacts the frame near the swing bearing.

Step 2: Electrical Testing
Using a digital multimeter, measure solenoid valve coil resistance—specification is typically 18-22 ohms at room temperature. Check supply voltage at the connector with ignition on (should read battery voltage, approximately 12V). Test for continuity between the ECM connector pins and the solenoid valve connector to identify wiring breaks.

Step 3: Component Testing
If wiring checks pass, bench-test the solenoid valve by applying 12V directly—it should produce an audible click and show consistent resistance. For used excavators, carefully clean all grounding points on the pump housing, as corroded grounds are a frequent culprit. Clear the code using Komatsu diagnostic software or a compatible scan tool after repairs.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC100-6 service manual and consider professional diagnostic support for complex electrical issues or component replacement.