U111786 - U111786 Private CAN Message Signal Invalid

U111786 Fault Detailed Definition

DTC Code (U111786) is defined as "Private CAN Message Signal Invalid", this fault code belongs to Generic Communication Bus category. In vehicle electronic architecture, this fault code indicates Adaptive Cruise Control Unit (ACC ECU) and its relying private CAN bus network exist abnormality at communication protocol level.

The "Private CAN" in system usually refers to non-public dedicated CAN channel used for high-speed data transmission between internal subsystems. When content check of message frame defined on this channel fails, expected message timeout occurs, or data validity determination does not match control unit logic, system records this code. This does not mean physical lines are completely disconnected, but means in a given communication session, controller received signals cannot meet expected data integrity standards.

Common Fault Symptoms

When DTC U111786 recorded and confirmed triggered, vehicle driving experience and dashboard feedback will present following specific manifestations:

• Adaptive Cruise System Function Fail: ACC active function immediately disabled, driver needs to take over speed control completely via pedals.
• System Status Feedback Abnormal: Instrument panel ACC indicator icon may light yellow or red warning light, indicating communication fault.
• Following Strategy Interrupted: Vehicle cannot execute preset automatic acceleration/deceleration logic, cruise control or adaptive following function fails.

Core Fault Cause Analysis

Targeting "Private CAN Message Signal Invalid" this core logic, technical breakdown from three dimensions of system architecture:

1. Hardware Component Level:

   • Involved ACC controller internal communication transceiver (Transceiver) abnormality or bus interface chip failure.
   • Gateway module or sensor nodes directly connected to private CAN network failed to transmit valid frame signals correctly.

2. Wiring/Connector Level:

   • Physical link connecting to Private CAN bus exists high impedance fault, causing signal level attenuation under specific thresholds.
   • Connector pin contact poor, pin short circuit or open circuit, affecting message data integrity transmission path.

3. Controller (Logic Operation) Level:

   • ACC control unit internal private CAN message parsing algorithm determination error.
   • Controller internal communication monitor detects message checksum error or frame format mismatch, thus determining signal invalid.

Technical Monitoring and Trigger Logic

Fault code U111786 judgment based on strict electrical and time sequence thresholds, control system will only mark this fault when all following conditions met:

• Power Supply Voltage Window: Controller power input voltage must be within normal working window range, i.e. $9V$~$16V$. If voltage below lower limit or above upper limit, system will preferentially record overvoltage/undervoltage fault rather than communication fault.

• Timing Monitoring Conditions: Fault judgment occurs after power-on initialization $3s$. Control system needs to start first round validity self-check on private CAN network in the 3rd second after vehicle power starts.

• Bus Status Logic: System detects Private CAN message invalid simultaneously, must confirm bus is not entering busoff state. Bus-off usually represents physical layer communication completely interrupted (such as nodes stop sending arbitration bits), and this fault specifically refers to message data invalidity under communication survival state.

• Software Mode Constraint: Only when Factory Mode Disabled, this fault determination logic will activate and record DTC. If in factory debugging mode, system enters special diagnostic configuration process, then ignoring regular validity checks to avoid false positives.