B1C1313 - Trunk Lock Motor Open Circuit

Depth Definition for DTC B1C1313 Trunk Lock Motor Open Circuit Fault

DTC B1C1313 is a key fault diagnostic code (BDC) targeting actuator circuit status in the Vehicle Body Control System (Body System). Under domain control architecture, this code specifically points to communication or physical connection abnormalities between the Left Domain Controller (LDC) and its controlled electric actuator. Specifically, "Open Circuit" means there is a high impedance or interruption state in the electrical loop from the controller output to the Trunk Lock Motor.

From system control logic perspective, this fault code records the failure of the current detection loop during trunk lock operation. When the controller instructs the motor to rotate to execute lock/unlock actions, the system expects to detect corresponding load current in the control loop. However, triggering B1C1313 indicates that the controller cannot identify the expected current flow within the specified monitoring time, which is typically judged at the hardware level as a physical connection interruption or internal coil open circuit of the motor, causing feedback loop failure, allowing the entire vehicle network to record this open circuit fault to stop relevant function driving and prevent control unit overload.

Common Fault Symptoms

When DTC B1C1313 is written into the on-board diagnostic system, the vehicle terminal will exhibit obvious functional degradation. These symptoms are not only warning messages on the instrument panel but also directly affect owners' daily driving experience:

• Back Door Lock Function Failure: This is the most direct manifestation. Whether triggered by in-vehicle switch, remote key, or automatic induction, the locking or unlocking action of the rear trunk door cannot be executed.
• Infotainment System Displays Error Messages: The vehicle information display system (Infotainment System) may show this component communication timeout or control failure fault code in the settings menu, causing relevant function icons to gray out or become unavailable.
• No Motor Rotation Feedback: When attempting to trigger lock actions, users might observe no mechanical response from the trunk lock actuator, accompanied by abnormal noises before entering safety protection mode.

Core Fault Cause Analysis

Based on original diagnostic data of B1C1313 and circuit logic, this fault can be caused by hardware or logical anomalies in the following three dimensions:

• Wiring and Connectors (Physical Connection Dimension): This is the most common external circuit interruption cause. The wiring harness between the trunk lock motor and the left domain controller may have broken lines, insulation layer damage due to wear leading to short/open circuit, or relevant connector pins oxidation/loosening causing poor contact. These physical defects prevent control signals or drive current from forming a complete loop.
• Trunk Lock (Actuator Hardware Dimension): The coil inside the trunk lock motor may be open (Open Winding), or the motor rotor may be mechanically stuck, preventing current flow completely and being misjudged by the controller as an open circuit. Additionally, excessive wear of carbon brushes inside the motor or damaged stator windings are fundamental causes leading to no current generation.
• Left Domain Controller (Logical Calculation Dimension): Faults in the drive circuit or current sampling module inside the control unit. Even if external lines and motor are normal, if the left domain controller cannot generate correct drive pulses or its ADC converter cannot correctly collect loop current signals, the system will erroneously record it as an open circuit fault.

Technical Monitoring and Trigger Logic

B1C1313 judgment logic is based on real-time dynamic monitoring of actuator load capability by vehicle control units. This fault code generation strictly follows the following monitoring rules:

• Monitoring Target: System continuously monitors the current value of the trunk lock motor control loop connected to the left domain controller output end. This is the core parameter for judging drive loop integrity.
• Operating Condition: Fault only triggers under specific execution states, i.e., when a request for "Trunk Lock Operation" is issued by users or system. If not in an activated state, the line remains in high impedance sleep mode, generating no monitoring data.
• Threshold Judgment and Trigger: Within a specific time period after drive motor starts, the control unit detects control loop current zero. Specific logic: When no current is detected ($I_{loop} \approx 0A$), and excluding normal situations like instruction not issued, system judges physical disconnection of the loop exists. Once satisfying above "when trunk lock works, detect control loop no current" condition, fault code is recorded immediately and stored.
• Diagnostic Result Recording: This logic ensures that only when motor cannot consume current in normal working mode will it be marked as motor open circuit, excluding false alarms from static voltage detection, ensuring high diagnostic accuracy.