What is Komatsu PC160LC-7 Fault Code S-16?

Fault Code S-16 on the Komatsu PC160LC-7 indicates a starter motor relay circuit malfunction or abnormal voltage detection in the starting system. This diagnostic trouble code (DTC) is triggered when the machine's Engine Control Module (ECM) detects irregular voltage signals or circuit resistance in the starter relay pathway, preventing proper engagement of the starter motor.

This code is critical for the PC160LC-7 because it directly affects the machine's ability to start reliably. The starter relay circuit acts as the electrical bridge between the ignition key switch and the starter motor. When this system malfunctions, the excavator may fail to crank entirely or experience intermittent starting issues that can strand operators on job sites. In used machines, this fault often indicates deteriorating electrical connections or component wear that requires immediate attention.

Common Symptoms

• Engine cranks slowly or fails to turn over when the key switch is activated
• Intermittent no-start conditions, especially during cold weather or after the machine sits overnight
• Clicking sound from the starter relay without engine engagement
• Monitor panel displays S-16 error code with potential warning light activation
• Battery drains faster than normal due to continuous relay engagement or parasitic draw

Potential Causes

The S-16 code on used PC160LC-7 excavators typically stems from age-related electrical degradation. Corroded or loose battery terminals create voltage drops that confuse the ECM's monitoring system. The starter relay itself may have burned contacts from repeated high-current cycling over thousands of operating hours.

Wiring harness issues are extremely common in this model year, particularly where the starter circuit harness passes near the engine block—heat and vibration cause insulation breakdown and wire chafing. The ignition key switch contacts wear out in high-hour machines, creating intermittent connections. Additionally, poor ground connections at the frame or engine block introduce resistance that triggers abnormal voltage readings.

In used equipment, previous repair attempts may have left improper splice connections or aftermarket relays with incompatible specifications.

How to Troubleshoot and Fix Code S-16

Step 1: Visual Inspection and Voltage Testing Begin by inspecting all battery cable connections and the starter relay location (typically mounted on the right side near the battery box). Clean any corrosion on terminals using a wire brush and dielectric grease. Using a digital multimeter, verify battery voltage reads 12.4-12.8V with the engine off and the key in the OFF position.

Step 2: Relay and Circuit Testing Access the starter relay connector and perform a continuity test with the key switch in the START position. The relay should show less than 0.5 ohms resistance across its contacts when energized. Check the control wire voltage (typically a small-gauge wire from the key switch)—it should read full battery voltage during cranking attempts. If voltage drops below 10V, trace back to find the resistance point.

Step 3: Harness Inspection and Component Replacement For used excavators, physically trace the starter circuit wiring harness from the relay to the starter motor, looking for chafed insulation, melted sections, or brittle wiring—common failure points on PC160LC-7 machines with 5,000+ hours. Inspect all connector pins for bent terminals or green corrosion. Replace the starter relay if internal contacts show pitting. If all wiring checks pass, test the key switch for proper contact closure using Komatsu diagnostic software or a compatible scan tool to monitor real-time relay command signals.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnosis for complex electrical issues or if you lack proper testing equipment.