What is Komatsu PC220-10 Fault Code CA1691?

Fault Code CA1691 indicates a communication error between the Engine Controller (ECM) and the Machine Controller (MCU) on the Komatsu PC220-10 excavator. This diagnostic trouble code (DTC) specifically signals that the CAN (Controller Area Network) bus communication has been interrupted or degraded between these two critical electronic control units.

The PC220-10 relies on continuous data exchange between the ECM (which manages engine performance, emissions, and fuel delivery) and the MCU (which oversees hydraulic functions, cab displays, and operational modes). When communication fails, the machine's integrated systems cannot coordinate properly, leading to performance degradation or complete operational shutdown. This fault is particularly critical because the PC220-10's advanced fuel efficiency and power management features depend entirely on seamless controller communication.

Common Symptoms

When Code CA1691 is active, operators typically experience:

• Warning light illumination on the monitor panel, often accompanied by a "Check Engine" or communication error message
• Reduced engine power or automatic derate mode, limiting RPM and hydraulic flow to protect the machine
• Intermittent or complete loss of dashboard display functions, including fuel gauge, temperature readings, or hour meter
• Erratic hydraulic response or inability to switch between work modes (Power, Economy, Breaker modes)
• Engine may start but immediately shut down or enter limp-home mode with severely limited functionality

Potential Causes

The most common technical reasons for CA1691 on used PC220-10 excavators include:

• Corroded or damaged CAN bus connectors at the ECM or MCU harness connection points, especially the 38-pin ECM connector
• Wiring harness chafing where the main harness runs along the right side of the engine bay near the turbocharger heat shield—a known wear point on this model
• Failed termination resistors within the CAN network (typically 120-ohm resistors at network endpoints)
• Water intrusion into controller housings, particularly the MCU located under the operator's seat, vulnerable in machines with cab floor damage
• ECM or MCU internal failure, more common in high-hour machines (8,000+ hours) or those exposed to extreme temperatures
• Loose or corroded ground connections at battery terminals or chassis ground points, disrupting communication signal integrity

How to Troubleshoot and Fix Code CA1691

Step 1: Initial Visual Inspection Begin by thoroughly inspecting the main wiring harness between the engine compartment and cab. Focus on the routing near the engine's right side where the harness passes the turbocharger. Look for melted insulation, abraded wires, or evidence of heat damage. Check all connector pins at both the ECM (mounted on the engine's left side) and MCU (under the operator's seat) for corrosion, bent pins, or moisture. On used excavators, connector corrosion is the leading cause of this fault.

Step 2: Test CAN Bus Continuity and Resistance Using a digital multimeter, disconnect both the ECM and MCU connectors. Measure resistance between CAN-High and CAN-Low wires (typically yellow and green wires at pin positions specified in the service manual). You should read approximately 60 ohms with both controllers disconnected, indicating proper termination resistors. A reading of 120 ohms suggests one terminator has failed; infinite resistance indicates an open circuit in the harness.

Step 3: Voltage and Signal Testing Reconnect the controllers and use the multimeter to verify 12V supply voltage at both ECM and MCU power pins with the key switch on. Check that both controllers share a common ground reference with less than 0.1V difference. If available, use Komatsu KOMTRAX diagnostic software or a compatible CAN bus scanner to monitor live communication packets and identify which controller is failing to transmit.

Step 4: Address Specific Failure Points For used machines, clean all connector terminals with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Replace any damaged harness sections using OEM-spec shielded CAN cable. If harness routing shows signs of previous rubbing, relocate and secure with proper standoffs. Test termination resistors individually and replace if readings exceed 120-130 ohms. Only after eliminating all wiring and connection issues should you consider ECM or MCU replacement, as controllers rarely fail without external cause.

Disclaimer: This guide provides general troubleshooting information for educational purposes. Always consult the official Komatsu PC220-10 service manual and consider professional diagnostic assistance, especially when dealing with electronic control systems. Improper repairs may cause additional damage or safety hazards.