What is Komatsu PC120LC-6 Fault Code S-16?

Fault Code S-16 on the Komatsu PC120LC-6 indicates a malfunction in the main pump pressure sensor circuit or an abnormal pressure signal from the hydraulic main pump system. This code is part of Komatsu's advanced hydraulic monitoring system that constantly measures pump discharge pressure to optimize performance and prevent component damage.

The main pump pressure sensor monitors hydraulic pressure output and sends voltage signals to the Electronic Control Module (ECM). When the ECM detects voltage readings outside the normal operating range (typically 0.5-4.5V), or when the sensor fails to respond, it triggers S-16. For the PC120LC-6, this is critical because the machine relies on precise hydraulic pressure feedback to regulate engine RPM, implement response, and prevent over-pressure conditions that could damage seals, hoses, or the pump itself.

Common Symptoms

• Erratic hydraulic performance with sudden power loss during digging or lifting operations
• Engine derate or limited RPM as the ECM enters protective mode to prevent pump damage
• Warning light illumination on the instrument panel, often accompanied by intermittent beeping
• Sluggish implement movement or inconsistent boom/arm speed, particularly under load
• Fluctuating hydraulic pressure visible on machines equipped with pressure gauges

Potential Causes

On used PC120LC-6 excavators, S-16 typically stems from age-related deterioration. The pressure sensor connector (located near the main control valve) is prone to corrosion from moisture intrusion and hydraulic mist. Wiring harness chafing occurs where the sensor cable passes near the pump mounting bracket—a known wear point on this model.

Other common causes include sensor drift from years of heat cycling, contaminated hydraulic fluid creating pressure spikes that damage sensor internals, and faulty ECM grounds causing voltage irregularities. Less frequently, actual main pump wear producing abnormal pressure patterns can trigger the code.

How to Troubleshoot and Fix Code S-16

Step 1: Visual Inspection Inspect the pressure sensor and its 3-pin connector for oil contamination, corrosion, or pushed-back pins. On used machines, check the entire wiring harness from sensor to ECM for abrasion points, especially where it contacts metal edges.

Step 2: Electrical Testing Using a digital multimeter, backprobe the sensor connector with the key on, engine off. Verify supply voltage (typically 5V) and ground continuity (less than 1 ohm resistance). Check sensor output voltage at idle and under load—it should increase proportionally with hydraulic demand.

Step 3: Sensor Replacement and Calibration If voltage readings are erratic or stuck, replace the main pump pressure sensor (Komatsu Part #7861-93-1650). After installation, use Komatsu diagnostic software (KOMTRAX or equivalent) to clear codes and verify sensor calibration parameters match factory specifications.

Step 4: Hydraulic System Verification If the code persists after sensor replacement, test actual pump pressure with a mechanical gauge (test port on control valve). Compare readings against service manual specs—significant deviation indicates pump wear requiring professional rebuild.

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Disclaimer: This guide provides general diagnostic procedures. Always consult the official Komatsu service manual and consider professional assistance for complex hydraulic or electronic repairs.