B225871 - B225871 Sunshade Switch Sticky

B225871 Sunshade Switch Sticking Fault Diagnostic Technical Note

# Fault Depth Definition

In smart vehicle electrical architecture, fault code B225871 (DTC) indicates an abnormal signal status on the communication link between the Body Domain Controller and the sunshade actuator. This code explicitly points to a "switch sticking" phenomenon, meaning the control unit detects that pulse feedback signals from the sunshade operation interface fail to switch correctly with physical action and remain at a single logic level for an extended period. This definition covers mechanical binding at the hardware level and logical adhesion at the electrical level, indicating that the left domain controller cannot receive physical location change signals conforming to expected timing, thereby affecting the closed-loop control precision of the body comfort system.

# Common Fault Symptoms

When system monitoring detects the B225871 code trigger, user-side and in-vehicle electronic systems typically exhibit the following perceptible manifestations:

• Sunshade actuator function responds sluggishly or is completely lost, unable to perform up/down operations via manual commands on the central control screen.
• Instrument cluster displays body system warning information, indicating sunshade mechanism status anomaly.
• System enters a protective failure mode, temporarily masking automatic logic dependent on switch feedback (such as light sensor linkage).
• Physical switch operation is inconsistent with actual motor response status, showing "no reaction upon press" or "repeat execution" phenomena.

# Core Fault Cause Analysis

Based on system architecture and signal flow direction, the root cause of this fault can be summarized into hardware or logic abnormalities in the following three dimensions:

• Hardware Component Failure (Sunshade Switch Fault): Refers to oxidation, wear, or physical jamming of internal contacts within the micro-switch or Hall sensor inside the sunshade operation end, preventing expected level transitions during mechanical pressing.
• Wiring Connection Anomaly (Harness or Connector Fault): Includes short circuit grounding due to insulation layer damage between control harness and switch, or signal pathway high impedance interruption caused by connector terminal pin withdrawal or poor soldering, leading the controller to misjudge it as "sticking".
• Controller Logic Computation Error (Left Domain Controller Fault): Refers to internal adhesion occurring in the input sampling circuit or drive logic inside the body domain controller, preventing correct identification of external signal instantaneous state changes, resulting in determination of input port function failure.

# Technical Monitoring and Trigger Logic

Vehicle electronic systems trigger fault code B225871 by monitoring signal integrity in real-time, with core logic as follows:

• Monitoring Target: System continuously monitors input signal voltage value and duty ratio changes of the sunshade switch, focusing on verifying whether signal status matches execution commands.
• Judgment Threshold and Logic: During motor drive action, the control unit compares expected signal transitions with actual readings. If the system detects switch signals maintaining a single logic level state and unable to flip state within specified time limits upon button operation, it is judged as signal sticking.
• Trigger Conditions: This fault activation judgment is conducted only during dynamic monitoring processes of body system power-on initialization and motor drive action, ensuring accurate capture of signal anomalies whether vehicle is moving or stationary, preventing false reports.