What is Komatsu PC100-6 Fault Code S-13?

Fault Code S-13 on the Komatsu PC100-6 indicates a malfunction in the fuel injection system's governor solenoid circuit. This code specifically signals an abnormal voltage or current condition in the electronic governor control circuit, which regulates engine speed and fuel delivery through the injection pump's solenoid valve.

The governor solenoid is critical for maintaining precise engine RPM control on the PC100-6's diesel engine. When this circuit fails, the Engine Control Module (ECM) cannot properly modulate fuel delivery, potentially causing engine speed instability or performance limitations. For used excavators, this fault often stems from age-related electrical degradation rather than catastrophic component failure.

Common Symptoms

• Engine speed fluctuations or hunting (RPM surging up and down) during idle or operation
• Reduced power output or inability to reach maximum engine RPM under load
• Warning light activation on the instrument panel (typically amber/yellow maintenance indicator)
• Engine derating where maximum throttle produces limited response
• Hard starting or extended cranking periods, especially when cold

Potential Causes

The S-13 code typically results from electrical circuit issues in aging PC100-6 excavators:

• Damaged wiring harness between the ECM and injection pump, particularly at flex points near the engine mounting where vibration causes wire insulation breakdown
• Corroded or loose connectors at the governor solenoid plug or ECM terminals due to moisture infiltration
• Failed governor solenoid within the injection pump assembly (less common but possible after 5,000+ hours)
• ECM internal fault in the solenoid driver circuit (rare, but observed in high-hour machines)
• Voltage supply issues from corroded ground connections or battery terminal oxidation affecting circuit reference voltage

How to Troubleshoot and Fix Code S-13

Step 1: Visual Inspection Examine the wiring harness routing from the ECM (located behind the operator's cab) to the injection pump. On used PC100-6 excavators, check for harness contact points against the engine block or hydraulic lines. Look for chafed insulation, particularly at the harness support clamps near the fuel filter. Inspect all connector pins for corrosion (green/white oxidation) and ensure positive locking.

Step 2: Electrical Testing Using a digital multimeter, disconnect the governor solenoid connector at the injection pump. Measure resistance across the solenoid terminals—specification is typically 18-25 ohms at 20°C. Test continuity of the wiring between the ECM connector (Pin 23 and Pin 24 on PC100-6) and the solenoid plug. Resistance should be under 1 ohm. Check for short circuits to ground by measuring between each wire and chassis ground (should show infinite resistance).

Step 3: Voltage Supply Verification Reconnect the harness and backprobe the solenoid connector with ignition ON, engine OFF. You should measure battery voltage (12-14V) on the supply wire. During cranking, verify the ECM is pulsing the ground circuit using a test light or oscilloscope—the signal should modulate at approximately 50-200 Hz.

Step 4: Component Replacement Priority For used excavators, begin with the most failure-prone items: clean/replace corroded connectors first, then replace damaged harness sections using heat-shrink solder connectors. If electrical circuits test correctly, replace the governor solenoid assembly (Komatsu Part# 6211-71-8120). ECM replacement should be the final option after confirming all external circuits are fault-free.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu PC100-6 service manual and consider professional diagnostic support, especially when dealing with fuel system components. Improper repairs can cause serious engine damage or safety hazards.