What is Komatsu PC110-8M0 Fault Code CA731?

Fault Code CA731 indicates a communication error between the Engine Controller (ECM) and the Hydraulic Pump Controller (HPC) on the Komatsu PC110-8M0 excavator. This code specifically signals that the CAN (Controller Area Network) communication line has lost signal integrity or experienced a timeout between these two critical control modules.

This fault is particularly serious for the PC110-8M0 because the ECM and HPC must constantly communicate to optimize engine speed with hydraulic demand. When this communication breaks down, the machine cannot properly match engine power to hydraulic system requirements, resulting in poor performance and potential component damage. The PC110-8M0's advanced load-sensing hydraulic system relies heavily on this data exchange to deliver the fuel efficiency and responsiveness Komatsu operators expect.

Common Symptoms

• Warning lamp illumination on the monitor panel, often accompanied by a specific communication error message
• Reduced hydraulic power or sluggish boom/arm/bucket response, especially under load
• Engine RPM fluctuations that don't correspond to joystick input or load changes
• Intermittent loss of multiple functions simultaneously, distinguishing this from single-circuit hydraulic failures
• Machine may enter derate mode, limiting engine power to protect components from uncoordinated operation

Potential Causes

The most common causes for CA731 on used PC110-8M0 excavators include:

• Corroded or damaged CAN bus connectors at the ECM or HPC—particularly the 38-pin connector at the ECM location under the operator cab
• Wiring harness chafing along the chassis routing path between the engine compartment and hydraulic pump area, especially where the harness passes near the swing motor mount
• Failed terminating resistor on the CAN network (120-ohm resistor specification)
• ECM or HPC module failure, though less common than wiring issues in used machines
• Voltage irregularities from aging battery cables or poor grounding at the controller mounting points

How to Troubleshoot and Fix Code CA731

Step 1: Visual Inspection of CAN Network Components Begin by inspecting all connectors between the ECM and HPC. On used excavators, pay special attention to the main harness routing near the swing bearing and along the chassis frame where vibration causes wear. Look for green corrosion on pins, pushed-back pins, or moisture intrusion in connector boots.

Step 2: Test CAN Bus Integrity Using a multimeter, check the terminating resistance across the CAN-High and CAN-Low lines at the ECM connector (should read approximately 60 ohms with controllers connected, 120 ohms with one disconnected). Disconnect one controller at a time and verify resistance remains consistent, indicating proper termination resistors are present.

Step 3: Voltage and Signal Testing With Komatsu diagnostic software (KOMTRAX PLUS or equivalent), monitor live CAN bus traffic while operating the machine. Check for intermittent dropouts or error frames. Also verify the CAN power supply voltage (typically 5V reference) at both controllers remains stable between 4.75-5.25V during operation.

Step 4: Harness and Ground Verification For used machines, thoroughly inspect the ground connections at both the ECM and HPC mounting locations. Clean all ground contact surfaces to bare metal and apply dielectric grease. Check harness continuity from end to end on both CAN-High and CAN-Low wires, looking for readings above 5 ohms which indicate damaged conductors.

Disclaimer: This guide provides general troubleshooting direction for fault code CA731. Always consult the official Komatsu PC110-8M0 service manual and consider professional diagnostic assistance for complex electrical issues. Improper testing can damage sensitive electronic control modules.