Komatsu PC220-8M0 Fault Code CA155: Technical Guide

What is Komatsu PC220-8M0 Fault Code CA155?

Fault Code CA155 indicates a malfunction in the machine's CAN (Controller Area Network) communication system, specifically a communication error between the engine controller (ECM) and the machine controller (MCU). This code signals that the two primary control units are unable to properly exchange data over the CAN bus network, which is critical for coordinated operation of the excavator's systems.

This fault is particularly serious on the PC220-8M0 because the SAA6D107E-1 engine relies on constant communication between controllers to manage fuel injection timing, hydraulic pump control, and emission systems. When this communication fails, the machine cannot operate efficiently or may enter a protective derate mode to prevent potential damage.

Common Symptoms

• Warning light illumination on the dashboard, typically the engine malfunction light or master caution indicator
• Reduced engine power or automatic engine speed limitation (derate mode) preventing normal operation
• Erratic hydraulic response or sluggish boom/arm movements due to improper pump control signals
• Intermittent shutdowns or failure to start, especially after the machine has warmed up
• Multiple fault codes appearing simultaneously, indicating widespread communication issues across systems

Potential Causes

The most common causes of CA155 in used Komatsu PC220-8M0 excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at flex points near the engine mounting or chassis frame where vibration causes wire chafing
• Loose or corroded connectors at the ECM or MCU, especially the 120-ohm terminating resistor connections at either end of the CAN bus
• Failed terminating resistors within the CAN network (should measure 60 ohms across CAN-High and CAN-Low when both are present)
• ECM or MCU internal failure, though less common than wiring issues in used machines
• Voltage supply problems to either controller, typically caused by corroded ground connections or failing relays
• Aftermarket component interference, such as improperly installed monitoring systems tapping into the CAN network

How to Troubleshoot and Fix Code CA155

Step 1: Visual Inspection of Wiring and Connectors

Begin by inspecting the CAN bus harness running between the engine ECM (located on the right side of the engine) and the main controller. On used excavators, pay special attention to harness routing near the engine mounts, turbocharger heat shields, and hydraulic lines where heat and vibration cause insulation degradation. Check all connectors for corrosion, bent pins, or moisture intrusion.

Step 2: Test CAN Bus Resistance

Using a digital multimeter, disconnect both the ECM and MCU connectors. Measure resistance between CAN-High and CAN-Low terminals at the harness side. You should read approximately 60 ohms, indicating both 120-ohm terminating resistors are functioning. A reading of 120 ohms means one resistor has failed; an open circuit indicates both have failed or there's a wiring break.

Step 3: Check Voltage and Ground Circuits

Verify that both controllers are receiving proper battery voltage (12-14V with ignition on) and have solid ground connections. Corroded ground straps are extremely common on used machines. Check voltage at ECM pin terminals using the Komatsu KOMTRAX diagnostic software or a compatible scan tool to identify which controller is dropping communication.

Step 4: Perform CAN Signal Integrity Test

If wiring and resistance checks pass, use an oscilloscope or the Komatsu diagnostic software to monitor CAN-High and CAN-Low signal activity. Proper CAN communication shows voltage differential patterns between 2.5V and 3.5V. Absence of signal activity from one controller identifies the failed component.

Step 5: Address Findings and Clear Codes

Replace damaged harnesses, clean corroded connections with electrical contact cleaner, and ensure all terminating resistors are functioning. On used excavators, always apply dielectric grease to connectors after cleaning to prevent future corrosion. After repairs, clear codes using diagnostic software and perform a stationary regeneration test to verify proper communication restoration.

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Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Komatsu service manual for your specific machine serial number and consider engaging a certified Komatsu technician for complex electrical diagnostics and controller replacement procedures.