Komatsu PC110-7 Fault Code S-2: Meaning, Symptoms, and Repair Guide

What is Komatsu PC110-7 Fault Code S-2?

Komatsu PC110-7 Fault Code S-2 indicates a malfunction in the engine controller (ECM) communication circuit or a failure in the controller's internal monitoring system. This code specifically points to an abnormality detected during the ECM's self-diagnostic routine, which monitors the integrity of its internal circuits and external communication pathways.

The S-2 code is particularly critical because the engine control module (ECM) serves as the brain of the excavator's diesel engine, managing fuel injection timing, air-fuel ratios, and emissions controls. When this fault activates, the machine may enter a protective derated mode to prevent engine damage, significantly impacting jobsite productivity on used machines where electronic component aging is common.

Common Symptoms

When fault code S-2 is active on your PC110-7, operators typically experience:

• Warning lamp illumination on the instrument panel with possible simultaneous alarm buzzer activation
• Engine power loss or limited RPM range as the ECM enters protective derate mode
• Intermittent engine stalling or difficulty restarting, particularly after the machine has warmed up
• Erratic engine behavior including irregular idling or sudden RPM fluctuations
• Complete shutdown in severe cases where the ECM fails to maintain safe operating parameters

Potential Causes

The S-2 fault code on used PC110-7 excavators typically stems from:

• ECM internal circuit failure due to age-related capacitor degradation or solder joint failures common in machines with 5,000+ operating hours
• Corroded or loose wiring harness connections at the ECM connector, especially where the harness routes near the engine block (heat exposure zone)
• Water intrusion into the ECM housing through damaged seals, prevalent in machines operated in wet conditions
• Failed power supply circuit including damaged main relay or blown fuses in the ECM power distribution
• Damaged communication wiring between the ECM and instrument cluster, particularly at known rub points near the operator's cab pivot

How to Troubleshoot and Fix Code S-2

Step 1: Visual Inspection and Connection Check Begin by disconnecting the battery negative terminal for safety. Locate the ECM (typically mounted under the operator's cab or near the hydraulic pump). Inspect the main wiring harness connector for corrosion, pushed-back pins, or moisture. On used excavators, pay special attention to connector seal integrity—white or green corrosion indicates water intrusion. Clean all connections with electrical contact cleaner and apply dielectric grease.

Step 2: Power Supply Verification Using a digital multimeter, check for proper voltage at the ECM power supply pins (consult your service manual for pin identification). You should read battery voltage (approximately 24V) on the main power supply pin with the key switch on. Check the ECM ground circuits for resistance—readings above 1 ohm indicate poor grounding requiring cleaning or replacement of ground straps.

Step 3: Communication Circuit Testing If power supply checks pass, test the CAN communication lines between the ECM and instrument panel. Measure resistance across the communication pair—typically showing 60 ohms with both devices connected (terminating resistor value). Inspect wiring near known chafe points where the harness crosses structural members.

Step 4: ECM Replacement Consideration If all external circuits test normal, the ECM internal failure is likely. For used machines, consider sending the ECM to a rebuilding specialist before purchasing new—potential savings of 60-70%. Replacement requires software reprogramming using Komatsu diagnostic software (KOMTRAX or authorized dealer equipment).

---

Disclaimer: This guide provides general troubleshooting information. Always consult your Komatsu service manual and consider professional diagnosis, especially when dealing with critical electronic systems. Improper repairs may cause additional damage or safety hazards.