What is Komatsu PC110-8M0 Fault Code 989N00?

Fault Code 989N00 on the Komatsu PC110-8M0 excavator indicates an abnormal signal or malfunction in the machine's exhaust temperature sensor system, specifically related to the diesel particulate filter (DPF) regeneration circuit. This code typically appears when the exhaust gas temperature sensor fails to provide accurate readings to the Engine Control Module (ECM), preventing proper monitoring of DPF regeneration cycles.

This fault is critical because the PC110-8M0's emission control system relies on precise exhaust temperature monitoring to initiate and complete DPF regeneration. Without accurate temperature data, the ECM cannot properly manage soot burn-off cycles, potentially leading to DPF clogging, reduced engine performance, and eventual engine protection shutdowns. For used excavators, this code often surfaces due to sensor degradation or wiring issues common in machines with significant operating hours.

Common Symptoms

• Yellow engine warning light illuminated on the instrument panel with code 989N00 displayed
• Automatic DPF regeneration cycles failing to complete or initiate properly
• Noticeable black smoke from the exhaust during operation due to incomplete combustion
• Engine derate mode activated, limiting maximum RPM and hydraulic system performance
• Increased fuel consumption as the ECM attempts compensatory adjustments

Potential Causes

The most common technical causes for Code 989N00 on used PC110-8M0 excavators include:

• Exhaust temperature sensor failure due to carbon buildup or internal element degradation after extended service hours
• Corroded or damaged wiring harness connections at the sensor plug, especially where the harness routes near the exhaust manifold and experiences heat cycling
• Broken or frayed sensor wiring at known rub points along the engine frame rail where cable ties deteriorate on older machines
• ECM software calibration issues or corrupted fault memory requiring reprogramming
• DPF system contamination causing abnormal exhaust flow characteristics that affect sensor readings
• Poor electrical ground connections at the sensor mounting point due to rust or loosened hardware

How to Troubleshoot and Fix Code 989N00

Step 1: Visual Inspection Begin by locating the exhaust temperature sensor on the DPF inlet pipe. Inspect the sensor body for physical damage, carbon accumulation, or signs of exhaust leaks. Check the wiring harness from sensor to ECM for abrasion, melted insulation, or damaged connectors—pay special attention to areas where the harness contacts metal surfaces or heat shields.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals. Komatsu specifications typically require 150-300 ohms at room temperature (consult your service manual for exact values). Next, check for continuity in the wiring from sensor connector to ECM pin terminals. Measure voltage supply at the sensor connector with ignition on—you should read approximately 5 volts reference voltage from the ECM.

Step 3: Connector and Ground Verification For used excavators, inspect all electrical connectors for corrosion, bent pins, or moisture intrusion. Clean contacts with electrical contact cleaner and apply dielectric grease. Verify the sensor's ground circuit shows less than 0.5 ohms resistance to chassis ground. Check mounting bolt torque specifications.

Step 4: Component Replacement and Calibration If sensor tests fail specifications, replace with a genuine Komatsu exhaust temperature sensor (part-specific to PC110-8M0). After installation, clear fault codes using Komatsu diagnostic software (KOMTRAX) or an authorized scan tool. Perform a forced DPF regeneration cycle to verify proper sensor function and code resolution.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Komatsu service manual for your specific machine serial number. Complex ECM diagnostics and DPF system repairs should be performed by certified Komatsu technicians with proper diagnostic equipment.