What is Yanmar General Fault Code U1167-8?

Fault Code U1167-8 indicates a CAN communication error with the "Lost Communication With Engine Control Module (ECM)" with a signal rate/period fault modifier. This Diagnostic Trouble Code (DTC) means the main controller or display unit has lost or is receiving intermittent communication signals from the engine's ECM over the Controller Area Network (CAN) bus.

In Yanmar excavators, the CAN bus serves as the critical communication backbone linking the engine ECM, instrument cluster, and other control modules. When this communication pathway fails or experiences irregular signal timing, the machine cannot properly monitor engine parameters, coordinate systems, or display accurate operational data. This fault is particularly critical because it can trigger protection modes that limit machine performance or cause complete shutdowns to prevent potential damage.

Common Symptoms

• Warning lights illuminated on the instrument panel, including check engine or communication error indicators
• Intermittent or complete loss of engine parameter displays (RPM, coolant temperature, fuel level)
• Erratic gauge behavior with needles jumping or freezing unexpectedly
• Reduced engine power or derate mode activation as a protective measure
• Difficulty starting or the engine starting but immediately shutting down due to communication timeout

Potential Causes

The most common technical causes for U1167-8 on used Yanmar excavators include:

• Corroded or loose CAN bus connectors at the ECM, instrument cluster, or junction points throughout the harness
• Damaged CAN bus wiring due to harness rubbing against frame components, especially near articulation points or along the boom
• Failed terminating resistors at either end of the CAN network (typically 120-ohm resistors)
• ECM power supply issues including poor ground connections or voltage drops from aged wiring
• Water intrusion into connectors causing intermittent shorts or high resistance
• ECM internal failure (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code U1167-8

Step 1: Visual Inspection Thoroughly inspect all CAN bus harness connections between the ECM and instrument cluster. Look for corroded pins, backed-out terminals, or damaged connector seals. On used excavators, pay special attention to harness routing near the engine mount points and cab pivot areas where vibration and movement cause wear.

Step 2: Check CAN Bus Continuity and Resistance Using a digital multimeter, disconnect power and measure resistance between CAN-High and CAN-Low wires at the ECM connector. You should read approximately 60 ohms (two 120-ohm terminating resistors in parallel). A reading significantly higher suggests an open circuit; lower readings may indicate a short.

Step 3: Verify Power and Ground Confirm the ECM has clean battery voltage (12-14V) at its power supply pin and solid ground connections (less than 0.1 ohms resistance to battery negative). Corroded ground straps are extremely common on older machines.

Step 4: Test CAN Signal Integrity If basic checks pass, use Yanmar diagnostic software or an oscilloscope to verify proper CAN bus signal voltage levels (2.5V differential between CAN-High and CAN-Low during communication). Irregular patterns indicate electrical interference or failing components.

Step 5: Replace Damaged Components Address identified issues: clean or replace corroded connectors, repair damaged harnesses with proper shielded wire, or replace the ECM if internal failure is confirmed through elimination testing.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Yanmar service manual for your specific model and consider professional diagnostic assistance for complex electrical issues.