B1CE713 - B1CE713 Reverse Lamp Drive Circuit Open Circuit Fault

Technical Definition of B1CE713 Reverse Lamp Drive Circuit Open Fault

Fault Depth Definition

B1CE713 (Reverse Lamp Drive Circuit Open Fault) is an electrical integrity anomaly determined by the Left Domain Controller for the reverse lamp lighting circuit system. In the vehicle control system architecture, this control unit is responsible for executing power stage output management for the rear tail lamp group and reverse lamps. When the system requests to light up the reverse lamp, the controller confirms the continuity of the drive circuit by monitoring load-end current feedback. "Open Circuit Fault" technically means the control unit cannot detect the expected drive current (Drive Current) flowing to the lamp load, or voltage feedback is abnormal, indicating that the physical connection or actuator element from the controller output terminal to the rear tail lamp is in an open state. This DTC not only reflects a single component failure but also involves the logical integrity verification of the entire power drive circuit under specific configurations.

Common Fault Symptoms

When the system determines this fault is true, the actual driving performance and instrument feedback of the vehicle usually present the following characteristics:

• Loss of Light Function: After turning on the low beam headlamp state and pushing the gear lever into reverse gear (or activating the reverse lamp switch signal), the rear position reverse lamps do not light up at all, leading to an increase in the rear field-of-view blind spots.
• No Response to Functional Request: The drive logic that sends the command to light up is active, but the execution terminal (lamp) does not receive effective power, manifesting as "separation of command and execution".
• Specific Conditions Triggered: The fault is captured and recorded as an active current fault by the system only when the vehicle is in a specific power state and the reverse signal is activated.

Core Fault Cause Analysis

For this DTC, from a technical perspective, its root causes can be categorized into three dimensions of hardware or connection problems:

• Wiring and Connector Failure: Including open circuit, short circuit or poor contact in the wiring harness between the rear tail lamp and the Left Domain Controller, as well as pin withdrawal oxidation leading to high resistance connections at connector pins. This is the external physical reason that prevents drive current transmission.
• Reverse Lamp Body Failure: Rear tail lamp bulb burnout, LED module failure or driver damage inside the lamp fixture, causing an open circuit condition even if the wiring is unbroken, judged by the system as a circuit breakage.
• Left Domain Controller Failure: Damage to power transistors (MOSFET) inside the control unit, abnormal driving logic circuitry or erroneous reports from data acquisition modules, leading to the system misjudging an open state or being unable to output drive signals.

Technical Monitoring and Trigger Logic

The determination of this DTC follows strict timing and threshold logic to ensure diagnostic accuracy. The monitoring system starts when vehicle power is on and execution conditions are met, with specific logic as follows:

• Monitoring Target: The system continuously collects drive circuit current values ($0A$) and controller supply voltage.
• Trigger Value Range: Fault determination requires the controller working voltage to be stable between $9V \sim 16V$, ensuring current monitoring within an effective voltage range, excluding misjudgments caused by low voltage inability to light up.
• Time Threshold: The system must continuously collect a drive current of $0$ for a continuous period of 3s; once this threshold is exceeded, it is confirmed as a fault state.
• Condition Limitations: Trigger logic must meet the following prerequisites:
  • Gear position signal is in "ON" position (Power or Ignition switch position);
  • System configuration identified as "Rear tail lamp configuration without LIN, or (with LIN rear tail lamp configuration and reverse lamps integrated into rear tail lamp configuration)";
  • Hardware platform limited to R1 Platform;
  • System receives a request signal to light up the reverse lamp.

Only when all monitoring conditions and trigger logic are met simultaneously, will the control unit mark the current state as B1CE713 Reverse Lamp Drive Circuit Open Fault.