What is Komatsu PC220-10 Fault Code CA691?

Fault Code CA691 indicates a communication error between the engine controller (ECM) and the machine controller (MC) on the Komatsu PC220-10 excavator. This code specifically triggers when the CAN (Controller Area Network) bus system detects intermittent or complete loss of data transmission between these two critical control modules.

The PC220-10 relies on constant communication between the ECM and MC to coordinate engine performance with hydraulic system demands, implement fuel-saving modes, and manage operational safety features. When this communication fails, the excavator cannot properly synchronize engine output with work functions, potentially leading to reduced productivity and component protection issues. This fault is particularly critical because it affects the machine's ability to optimize performance based on real-time load conditions.

Common Symptoms

When Code CA691 is active on your Komatsu PC220-10, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by an audible alarm
• Engine derating or limited RPM, preventing the machine from reaching full power output
• Erratic hydraulic response or sluggish attachment operation due to desynchronized engine-hydraulic coordination
• Intermittent loss of monitoring data on the display panel (temperature, pressure readings)
• Activation of limp mode, restricting machine operation to basic functions only

Potential Causes

The most common technical causes for CA691 in used PC220-10 excavators include:

• Corroded or damaged CAN bus connectors at the ECM or MC junction points (particularly X1 and X2 connectors)
• Wiring harness chafing along the frame rail between the engine compartment and cab, a known wear point after 5,000+ operating hours
• Failed terminating resistor on the CAN network (120-ohm resistor failure)
• ECM or MC internal communication circuit failure due to voltage spikes or moisture intrusion
• Loose or oxidized ground connections at G101 (engine block ground) or G201 (frame ground)
• Aftermarket component interference from improperly installed accessories disrupting CAN signals

How to Troubleshoot and Fix Code CA691

Step 1: Visual Inspection of CAN Bus Harness Begin by inspecting the main wiring harness running from the engine bay to the operator cab. On used excavators, check for abraded insulation where the harness passes through grommets or contacts metal edges. Pay special attention to the harness routing near the hydraulic pump—heat and vibration cause premature wear here. Disconnect and inspect all CAN connectors for green corrosion, bent pins, or moisture.

Step 2: Verify CAN Bus Communication with Diagnostic Software Connect Komatsu KOMTRAX diagnostic software or a compatible CAN bus analyzer to the service port. Check for proper CAN-H and CAN-L voltage levels (should read approximately 2.5V at rest, with differential voltage of 2V during communication). Use a multimeter to verify terminating resistance between CAN-H and CAN-L terminals—you should read approximately 60 ohms with both controllers connected (two 120-ohm resistors in parallel).

Step 3: Test Ground Circuits and Power Supply Measure ground integrity at both ECM and MC mounting locations. Resistance to battery negative should be less than 0.5 ohms. Check power supply voltage at both controllers—should be stable 24V DC. For used machines, remove and clean all ground terminals, applying dielectric grease before reconnection.

Step 4: Component Isolation Testing If communication remains interrupted, disconnect the MC connector and check if the ECM maintains internal diagnostics (indicating ECM functionality). Then reconnect and disconnect the ECM to isolate which controller has failed communication circuits. On older units, ECM internal circuit degradation is more common than MC failure.

Step 5: Replace or Repair Identified Components Replace damaged harness sections rather than attempting tape repairs on CAN circuits—signal integrity is critical. If a controller is faulty, ensure replacement units match the software version to avoid incompatibility issues common in used equipment retrofits.

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Disclaimer: This guide provides general diagnostic procedures for Komatsu PC220-10 fault code CA691. Always consult the manufacturer's official service manual and consider engaging a certified Komatsu technician for complex electrical diagnostics, especially when dealing with critical safety systems or before replacing expensive components like control modules.