What is Komatsu PC210LC-7 Fault Code S-15?

Komatsu PC210LC-7 Fault Code S-15 indicates a malfunction in the engine water temperature sensor circuit. This code triggers when the Engine Control Module (ECM) detects an abnormal voltage signal from the coolant temperature sensor, typically outside the expected range of 0.2-4.8 volts.

The water temperature sensor monitors engine coolant temperature and sends continuous analog signals to the ECM. This data is critical for fuel injection timing, idle speed control, and engine protection systems. On the PC210LC-7, this sensor directly influences hydraulic oil warm-up functions and prevents the engine from entering high-load operations when coolant temperatures are unsafe. When S-15 appears, the ECM may default to fail-safe mode, limiting machine performance to prevent catastrophic engine damage.

Common Symptoms

• Warning light illuminated on the instrument cluster, often accompanied by an audible alarm
• Engine runs in derate mode with reduced power output and slower hydraulic response
• Hard starting or extended cranking time, especially in cold weather conditions
• Engine idling roughly or hunting between RPM ranges during warm-up
• Inaccurate temperature gauge readings showing erratic fluctuations or stuck at cold/hot extremes

Potential Causes

The most common causes of S-15 on used PC210LC-7 excavators include:

• Failed coolant temperature sensor due to internal resistance drift or element corrosion (typical after 5,000+ operating hours)
• Damaged wiring harness near the thermostat housing where vibration causes wire insulation to fray against sharp edges
• Corroded or loose connector pins at the sensor plug, particularly on machines exposed to wet or marine environments
• ECM internal fault (less common) where the voltage reference circuit develops issues
• Coolant contamination causing sensor tip buildup and inaccurate readings
• Aftermarket sensor incompatibility if previous owners installed non-OEM replacement parts

How to Troubleshoot and Fix Code S-15

Step 1: Visual Inspection Begin by locating the coolant temperature sensor on the engine block near the thermostat housing. Inspect the entire wiring harness from sensor to ECM for obvious damage, chafing, or oil/coolant contamination. On used excavators, check for worn insulation where harnesses contact frame members or vibrate against engine components.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure resistance across sensor terminals. At 68°F (20°C), resistance should read approximately 2,000-3,000 ohms (consult service manual for exact specifications). Test connector pins for corrosion and verify harness continuity to the ECM using the machine's wiring diagram.

Step 3: Voltage Signal Check With ignition on and sensor connected, backprobe the signal wire at the connector using a multimeter. The voltage should change smoothly as engine temperature rises (typically 3-4V cold, dropping to 0.5-1V hot). Erratic or out-of-range readings indicate sensor replacement is needed.

Step 4: Replacement and Verification Install a genuine Komatsu OEM sensor (part number 6732-81-3140 or equivalent) using proper torque specifications. Clear the fault code using Komatsu diagnostic software (KOMTRAX or compatible scan tool) and verify S-15 does not return after a complete heat cycle.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual and consider professional diagnostic assistance for complex electrical issues or if unfamiliar with high-voltage systems.