What is Yanmar General Fault Code U1167?

Fault Code U1167 indicates a CAN Communication Bus Error between the Engine Control Module (ECM) and other machine control systems. This diagnostic trouble code (DTC) signals that the Controller Area Network (CAN) data link is experiencing communication failures, preventing proper information exchange between critical electronic control units.

In Yanmar excavators, the CAN bus network serves as the central nervous system, allowing the ECM, instrument cluster, hydraulic controllers, and emissions systems to communicate seamlessly. When U1167 appears, it means data packets are being lost, corrupted, or delayed beyond acceptable parameters. This is particularly critical because modern Yanmar machines rely on real-time CAN communication for proper fuel injection timing, hydraulic response, diagnostic functions, and emissions compliance. On used equipment, this fault often stems from environmental damage or age-related degradation of electrical components.

Common Symptoms

• Warning lights illuminated on the instrument panel, particularly the check engine light and potentially multiple system alerts simultaneously
• Erratic instrument cluster behavior, including flickering gauges, incorrect readings, or complete gauge failure
• Reduced engine performance or activation of derate mode, limiting power output to protect the engine
• Intermittent loss of hydraulic functions or delayed response from attachments due to communication gaps
• Inability to retrieve diagnostic codes or connect diagnostic tools properly to the machine's systems

Potential Causes

The most frequent causes of U1167 on used Yanmar excavators include:

• Damaged or corroded CAN bus wiring harness, especially at known rub points near the engine mounting brackets, boom pivot areas, or where harnesses pass through the chassis
• Loose or corroded electrical connectors at the ECM, instrument cluster, or intermediate junction boxes exposed to moisture intrusion
• Failed termination resistors at either end of the CAN network (typically 120-ohm resistors that maintain proper signal integrity)
• ECM or secondary controller failure, though less common than harness issues in used machines
• Aftermarket accessories improperly spliced into the CAN network, creating impedance mismatches or signal interference
• Battery voltage irregularities or poor grounding causing unstable reference voltages for CAN communication

How to Troubleshoot and Fix Code U1167

Step 1: Visual Inspection Begin with a thorough physical examination of all CAN bus wiring harnesses. On used excavators, focus on areas where cables route near moving components, sharp edges, or heat sources. Inspect all connectors for green corrosion, pushed-back pins, or moisture contamination. Check the main ECM connector and instrument cluster connections first, as these are common failure points.

Step 2: CAN Bus Resistance Testing Disconnect the battery and use a digital multimeter to measure resistance across the CAN-High and CAN-Low terminals at the diagnostic connector. You should read approximately 60 ohms with all modules connected (indicating two 120-ohm termination resistors in parallel). A reading significantly higher suggests an open circuit; lower readings may indicate a short circuit or incorrect termination.

Step 3: Voltage and Signal Testing With the ignition on (engine off), measure voltage on CAN-High (should read approximately 2.5-3.5V) and CAN-Low (should read approximately 1.5-2.5V) relative to chassis ground. These voltages should be relatively stable. Significant fluctuation indicates communication attempts with errors. Use Yanmar-specific diagnostic software if available to monitor live CAN bus traffic and identify which module is failing to communicate.

Step 4: Termination Resistor Verification Locate and test both termination resistors in the network. These are typically found at the ECM and the furthest module (often the instrument cluster). Each should measure 120 ohms independently. Failed or missing resistors cause signal reflection and data corruption.

Step 5: Component Isolation If harness and termination tests pass, systematically disconnect non-critical modules one at a time to identify a potentially faulty controller causing bus disruption. On used machines, aftermarket monitors or third-party telematics devices are frequent culprits.

Critical for Used Equipment: Before replacing expensive modules, thoroughly clean all ground connections and verify battery voltage remains above 12.5V. Age-related corrosion on ground straps creates voltage reference problems that mimic communication failures. Check for previous repairs where wire splices may have been improperly soldered or taped, creating high-resistance joints.

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Disclaimer: This guide provides general troubleshooting information for Yanmar excavators. CAN bus diagnostics can be complex, and improper repairs may cause additional system damage. Always consult the official Yanmar service manual for your specific model and consider engaging a certified Yanmar technician for proper diagnosis and repair, especially when dealing with electronic control systems.