Komatsu PC200-10 Fault Code CA428: Complete Diagnostic Guide

What is Komatsu PC200-10 Fault Code CA428?

Fault Code CA428 indicates a malfunction in the Engine Coolant Temperature (ECT) Sensor Circuit, specifically detecting an abnormally high voltage signal that suggests an open circuit or sensor failure. This code triggers when the Engine Control Module (ECM) receives voltage readings outside the acceptable range (typically above 4.8V) from the coolant temperature sensor circuit.

The ECT sensor plays a critical role in the PC200-10's engine management system by monitoring coolant temperature and relaying this data to the ECM. This information directly affects fuel injection timing, engine warm-up protocols, and exhaust gas recirculation (EGR) operation. When CA428 is active, the ECM defaults to a predetermined temperature value, which can compromise engine efficiency and emissions control.

Common Symptoms

• Check Engine Warning Light illuminated on the instrument panel with reduced engine performance
• Engine running rich or failing to reach optimal operating temperature efficiently
• Poor cold-start performance with excessive white or black smoke during initial operation
• Cooling fan running continuously at high speed regardless of actual engine temperature
• Reduced throttle response or activation of derate mode limiting engine RPM to protect components

Potential Causes

The CA428 code in used PC200-10 excavators typically stems from age-related and environmental factors:

• ECT sensor internal failure due to heat cycling and coolant contamination over thousands of operating hours
• Broken or corroded wiring in the sensor harness, particularly at flex points near the engine block where vibration causes wire fatigue
• Damaged connector pins or moisture intrusion at the ECT sensor plug, common in machines operating in wet or corrosive environments
• Worn harness insulation creating intermittent open circuits from rubbing against engine components
• ECM internal circuit degradation (rare but possible in high-hour machines)

How to Troubleshoot and Fix Code CA428

Step 1: Visual Inspection Begin by inspecting the ECT sensor and its wiring harness. The sensor is typically located on the engine coolant outlet housing. Check for physical damage, corrosion on the connector terminals, or coolant leakage around the sensor body. On used excavators, pay special attention to harness routing where wires contact hot engine surfaces or metal brackets.

Step 2: Electrical Testing Using a digital multimeter, disconnect the ECT sensor connector and measure resistance across the sensor terminals. Compare readings against Komatsu specifications (typically 2,000-3,000 ohms at 20°C). Check harness continuity from the ECM connector to the sensor plug, and verify ground circuit integrity shows less than 1 ohm resistance.

Step 3: Voltage Signal Check With the ignition on and sensor disconnected, measure voltage at the harness connector. You should see approximately 5V reference voltage from the ECM. If voltage is absent or incorrect, trace the wiring for breaks or inspect the ECM connections. For used machines, remove protective loom and inspect for green corrosion or wire strand breakage at connector crimp points.

Step 4: Component Replacement If testing confirms sensor failure, replace the ECT sensor using genuine Komatsu parts (Part# 6261-81-8210 or equivalent). Apply thread sealant and torque to specification. If harness damage is found, repair using proper crimping tools and heat-shrink connectors rated for engine compartment temperatures.

Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC200-10 service manual and consider professional diagnosis for complex electrical issues, especially when working with used equipment that may have undocumented modifications.