Komatsu PC1250-11R Fault Code D110KB: Complete Diagnostic Guide

What is Komatsu PC1250-11R Fault Code D110KB?

Fault Code D110KB indicates a malfunction in the engine coolant temperature sensor circuit or an abnormal coolant temperature reading detected by the engine control module (ECM). This code specifically relates to the SAA6D170E-5 engine's thermal management system, where the ECM has detected either an out-of-range voltage signal, an open circuit, or a short circuit in the coolant temperature sensor wiring.

This code is critical for the PC1250-11R because the ECM relies on accurate coolant temperature data to optimize fuel injection timing, control engine derating, and prevent catastrophic overheating. When D110KB is active, the engine may enter a protective derate mode, limiting horsepower and hydraulic performance to prevent engine damage.

Common Symptoms

When fault code D110KB is active, operators typically experience:

• Engine warning light illuminated on the monitor panel, often accompanied by an audible alarm
• Reduced engine power and hydraulic response due to ECM-imposed derate mode
• Erratic temperature gauge readings or gauge stuck at minimum/maximum positions
• Hard starting or rough idle, especially when the engine is cold
• Increased fuel consumption as the ECM defaults to a "safe" fuel map without accurate temperature data

Potential Causes

The most common technical causes for D110KB on used PC1250-11R excavators include:

• Coolant temperature sensor failure due to age-related degradation or thermal cycling damage
• Corroded or loose connector pins at the sensor harness (common on machines with 8,000+ operating hours)
• Damaged wiring harness from rubbing against engine components near the thermostat housing
• ECM internal fault affecting the sensor input circuit (rare but possible on high-hour machines)
• Contaminated coolant causing sensor element fouling or premature failure
• Poor ground connection at the sensor or ECM ground points

How to Troubleshoot and Fix Code D110KB

Step 1: Visual Inspection Begin by inspecting the coolant temperature sensor located near the thermostat housing on the cylinder head. Check the connector for corrosion, bent pins, or coolant intrusion. On used excavators, examine the wiring harness for chafing points where it routes near the engine block or exhaust manifold.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure its resistance. At 20°C (68°F), resistance should be approximately 2,000-3,000 ohms (consult Komatsu specifications). Check for continuity in the wiring from sensor to ECM. Measure voltage supply at the sensor connector with ignition on—you should see approximately 5 volts reference voltage from the ECM.

Step 3: Component Replacement and Verification If resistance values are out of specification or wiring shows damage, replace the faulty component. For used machines, always apply dielectric grease to connector pins to prevent future corrosion. After repairs, clear the code using Komatsu diagnostic software (KOMTRAX) and perform a test cycle to verify the fix.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.