U007388 - U007388 CAN Bus Shutdown Fault

U007388 CAN Bus Shutdown Fault Diagnostics Technical Description

Fault Depth Definition

DTC (Fault Code) U007388, defined in Chinese as CAN Bus Shutdown Fault, is a critical network status indicator within the vehicle communication system. Within the control architecture of Advanced Driver Assistance Systems (ADAS), this fault code indicates an abnormal interruption of the internal CAN communication link between the central gateway or domain controller and the relevant ADAS control modules.

From a technical logic perspective, the CAN Bus (Controller Area Network) serves as a high-priority physical layer transmission medium for real-time data exchange. The triggering of U007388 means that the receiver or transmitter of the control unit detects that the communication bus state has entered a "Bus Off" (bus shutdown) protection status. This typically involves an overflow of the underlying CAN protocol stack error counters, causing the control unit to temporarily stop active message transmission to prevent network congestion, thereby forcing disruption of ADAS-related data interactions. This signifies that the current communication link cannot meet continuous connection requirements on a hardware or electrical level.

Common Fault Symptoms

When U007388 is recorded and warning indicator lights illuminate, user-perceivable driving experience and dashboard feedback will undergo significant changes:

• Advanced Driver Assistance System Functionality Failure: Core ADAS suite components (such as Adaptive Cruise Control ACC, Lane Keeping Assist LKA, Automatic Emergency Braking AEB) will fail to activate or be forcibly closed by system logic; corresponding icons on the dashboard display may show as unavailable or in a warning state.
• Dashboard Warning Prompts: The vehicle's infotainment screen or multimedia center may pop up "Communication Fault", "Network Disconnected", or specific text prompts indicating module initialization failure.
• Related Functions Degradation: Data sharing functions dependent on the ADAS network (such as speed signal fusion, distance detection data) stop operating. The system may enter limp mode to ensure basic driving safety.

Core Fault Cause Analysis

Analyzing the underlying logic of this fault code, the root cause can be broken down into three technical dimensions:

1. Hardware Component Anomaly: Refers to a failure in the module itself on the ADAS network system. This includes damage to the communication chip inside the control unit, microcontroller reset exceptions, or unstable power supply from the Power Management Integrated Circuit (PMIC), causing the module to fail to correctly respond to CAN bus timing requirements and thus triggering an interruption of the communication link.

2. Harness and Connector Physical Connection: Covers physical integrity damage to the harness or connectors (Harness/Connector). Includes pin retreat due to vibration, cable wear or breakage, connector oxidation or corrosion from water ingress, causing interference or open circuit in CAN_H/CAN_L differential signal transmission, preventing the control unit from reading valid messages.

3. Controller Logic Judgment: Belongs to the calculation result of internal diagnostic logic within the domain controller or gateway. When hardware-level errors accumulate continuously and reach the system-set threshold, the control unit determines that the network state is unavailable, triggering DTC storage strategy and locking the fault code to prevent false reporting.

Technical Monitoring and Trigger Logic

The generation of this fault code follows strict timing and counting logic, with the control unit recording this fault only under specific conditions:

• Monitored Parameter Targets: The system continuously monitors the ADAS network bus status as well as the Busoff error counter value.
• Critical Threshold Markings:
  • The Bussoff Counter must exceed $8$ times, indicating communication errors have reached the maximum threshold.
  • The fault determination time window is $3\text{s}$ after system power-on initialization; if the above conditions are met within this period, it is determined as an instantaneous stable fault.
• Specific Operating Modes and Environmental Restrictions:
  • Operation Mode: This logic is only effective when the Factory Mode (Factory Mode) is in a closed/off state; in Factory Diagnostic Mode, the system may ignore such network protection states.
  • Trigger Timing: Only after stable vehicle power-on and passing $3\text{s}$ initialization delay will the system verify bus health; once the Busoff counter reaches $8$, it immediately locks the fault code and lights up the corresponding dashboard icons.