B1CE912 - B1CE912 Left Footwell Light Drive Circuit Short to Power Fault

Deep Definition of DTC B1CE912: Short to Supply in the Left Step Light Drive Circuit

DTC code B1CE912 is defined in the vehicle diagnostic system as "Left Step Light Drive Circuit Short to Supply". This code belongs to a specific control unit error within the Body Electrical Architecture, primarily involving the energy management logic of the left-side lighting system. In this system context, "Drive Circuit" refers to the electronic power stage pathway that controls the brightness of the Left Step Light, while "Short to Supply" specifically denotes an uncontrolled electrical connection between the load terminal and the Battery Positive Power Supply Rail during a non-conducting state.

This DTC reflects an abnormal electrical loop condition detected by the Body Domain Controller. Under normal conditions, the drive circuit manages lighting by controlling the on/off state of the ground path; when current is detected to return directly to the power terminal without passing through the load, or when the drive signal fails to cut off the power loop, the system classifies this as a High-Impedance Failure Mode (Short to Supply). This typically implies loss of hardware insulation or severe deviation in control logic.

Common Fault Symptoms

During vehicle operation, the following driving experience or instrument feedback characteristics indicate that DTC B1CE912 has been activated:

• Left Step Light Stay-On: Regardless of driver instruction to turn off lights or entering sleep mode, the left-side threshold and foot area illumination fixtures remain continuously lit, unable to respond to OFF signals.
• Abnormal Energy Consumption Indication: Due to the circuit being in a non-operational short-to-supply state, the total vehicle electrical load increases, which may manifest as faster battery drain or relevant electrical warning lights appearing on the instrument cluster.
• Control Logic Failure Feedback: When the driver attempts to adjust light brightness via physical switch or software control, the system is unable to execute the "OFF" action, and the light remains in a constant high-output state.

Core Fault Cause Analysis

Addressing B1CE912 fault phenomena requires principle-based troubleshooting and analysis of potential roots from the following three dimensions:

• Hardware Components (Left Step Light): Structural failure inside the Left Step Light assembly is one of the main causes of the short circuit. Specifically, this manifests as breakdown of the encapsulation insulation layer inside the light source (e.g., LED chip), or direct conduction formed between the positive and negative electrodes of the lamp bead within the light fixture. When a damaged light causes a short to supply, current will no longer be limited by the drive circuit, directly forming a return loop.
• Wiring/Harness/Connector Faults: Physical insulation failure appears in the wiring harness or related connectors connecting the Left Step Light. For example, abrasion of the wire harness outer sheath causing a short between the positive line and ground line; or in a long-term vibration environment, connector pin withdrawal or deformation of connector terminal metal sheets resulting in poor contact, creating parasitic conduction paths between originally isolated high voltage potential and ground potential.
• Controller Faults (Left Domain Controller): Anomaly occurs within the logic computation unit or output stage chip responsible for driving the Left Step Light inside the Left Domain Controller. When the PWM (Pulse Width Modulation) output pin of the controller loses switching capability due to internal component breakdown, or control logic judgment is erroneous, it may cause the drive signal to be forcibly locked at a high-level state, directly connecting the circuit end to the power side.

Technical Monitoring and Trigger Logic

Determination of DTC B1CE912 is based on dynamic comparison of real-time electrical parameters of the Left Step Light drive loop by the controller:

1. Monitoring Target: The control unit continuously monitors voltage drop (Voltage Drop) and current feedback values on the Left Step Light loop. The system focuses specifically on the potential state at the load terminal under "should be OFF" instructions.
2. Numerical Judgment Logic: When the system is in a drive cycle to extinguish lights, if the loop end voltage is detected to remain at power supply voltage level, or current values exceed preset thresholds, this is deemed to have short-circuit characteristics. Specific numerical ranges (e.g., difference between normal on-resistance and shorting resistance) are compared based on original calibration data; once actual measurement values consistently deviate from safe zones (such as $R_{measured} \approx R_{wire}$ with no load voltage drop), the judgment condition is triggered.
3. Specific Condition Trigger: Fault determination usually occurs after entering diagnostic ready state following ignition switch-on. The system will, within specific dynamic monitoring window periods (e.g., at the instant of light instruction switching while vehicle is stationary or driving), if abnormal conduction in the drive circuit to power terminals is detected continuously and duration meets calibration requirements, DTC B1CE912 fault code will be stored and relevant warning lights illuminated.