What is Komatsu PC110-8M0 Fault Code CA757?

Fault Code CA757 indicates a communication error or malfunction in the CAN (Controller Area Network) data line between the engine ECM (Engine Control Module) and the machine's main controller. This diagnostic trouble code specifically points to abnormal signal transmission or complete loss of communication on the CAN bus system that allows critical electronic components to exchange operational data.

The CAN bus communication system is the nervous system of modern Komatsu excavators, enabling the ECM, hydraulic controller, monitor panel, and other electronic modules to coordinate machine functions. When CA757 triggers, the PC110-8M0 cannot properly synchronize engine performance with hydraulic demands, leading to operational inefficiencies or complete shutdowns. This code is particularly critical because it affects multiple systems simultaneously, potentially causing the machine to enter a protective derate mode or fail to start entirely.

Common Symptoms

• Dashboard warning lights illuminate, often showing both engine and system error indicators simultaneously
• Reduced engine power or derate mode activation, limiting hydraulics and travel speed to prevent damage
• Intermittent loss of gauge functionality including RPM, temperature, or fuel level displays going blank
• Machine may not start or experiences unexpected shutdowns during operation
• Error messages on the monitor panel specifically referencing communication or system failures

Potential Causes

On used Komatsu PC110-8M0 excavators, CA757 typically stems from physical deterioration rather than component failure. The most common causes include:

• Corroded or loose CAN bus connectors at the ECM, especially the 38-pin main harness connector prone to moisture intrusion
• Damaged wiring harness along known rub points near the engine mounting brackets or cab pivot areas where cables flex repeatedly
• Failed termination resistors (120-ohm) at either end of the CAN network, often degraded in machines with 5,000+ operating hours
• ECM internal fault affecting the CAN transceiver circuit, though less common than harness issues
• Voltage irregularities from failing batteries or alternator problems creating signal interference on the data lines

How to Troubleshoot and Fix Code CA757

Step 1: Visual Inspection of Harness and Connectors Begin at the ECM location behind the operator cab. Disconnect the main 38-pin connector and inspect for green corrosion, bent pins, or moisture. Check the CAN-H (typically yellow) and CAN-L (typically green) wires throughout their routing for obvious damage, particularly where harnesses pass through bulkheads or near moving components. On used excavators, these wear points are the primary failure location.

Step 2: Test CAN Bus Termination and Resistance Using a quality digital multimeter, disconnect both ends of the CAN network (usually at the ECM and monitor controller). Measure resistance between CAN-H and CAN-L terminals—you should read approximately 60 ohms with both 120-ohm termination resistors in place. A reading of 120 ohms indicates one failed terminator; infinite resistance suggests a break in the data lines or both terminators have failed.

Step 3: Check Signal Voltage and Communication Reconnect all components and measure CAN-H and CAN-L voltages with ignition ON and engine running. Both lines should show approximately 2.5 volts DC at rest, fluctuating between 1.5V and 3.5V during active communication. Use Komatsu KOMTRAX diagnostic software or a compatible J1939 CAN scanner to monitor live data traffic and identify which module is dropping communication.

Step 4: Inspect Power Supply and Grounds Verify the ECM receives proper voltage (typically 24V on this model) and check all ground connections for tightness and corrosion. Poor grounds create voltage reference problems that disrupt CAN signal integrity, especially common in older machines operating in corrosive environments.

Disclaimer: This guide provides general troubleshooting direction for Komatsu PC110-8M0 fault code CA757. Always consult the manufacturer's official service manual and consider professional diagnostic assistance for complex electrical issues. Improper testing can damage sensitive electronic components.