B123F49 - B123F49 Unable to Acquire Temperature on Passenger Side PTC Core Surface

H2 DTC B123F49 Fault Depth Definition

B123F49 is a specific DTC regarding ambient temperature acquisition channels in the vehicle thermal management system, with its core involving the integrity verification of the passenger side PTC core surface temperature signal. In the whole-vehicle control logic architecture, this DTC indicates that the central control unit failed to successfully receive or parse real-time temperature feedback data from the passenger side heating assembly. This signal belongs to a key thermal management closed-loop parameter, mainly used to ensure output accuracy and safety of high voltage PTC air heaters under different load conditions. When the system detects a $0$ value, values out of valid range, or missing signals, it judges entry into this fault state. This definition emphasizes logical consistency between the acquisition object (passenger side PTC core surface) and the data the control unit expects to acquire; its failure will directly limit the active regulation function of the thermal management system.

Common Failure Symptoms

When the system records DTC B123F49 and executes protection strategies, drivers and occupants can observe the following specific manifestations in driving experience:

• High Voltage PTC Air Heater Function Failure: The related control unit will disable output commands, resulting in the passenger side being unable to provide expected auxiliary heating energy.
• Thermal Management Performance Degradation: The vehicle may automatically switch to a basic natural convection mode, losing active electrical heating adjustment capabilities, affecting cabin temperature rapid response.
• Instrument Feedback Abnormality: The instrument panel or infotainment system may display tip icons or warning text related to temperature sensor communication timeouts.

Core Failure Cause Analysis

Based on DTC logic and hardware architecture, the root causes leading to "unable to acquire temperature on passenger side PTC core surface" are mainly categorized into the following three dimensions:

• Hardware Component Failure: Core Temperature Sensor Failure, High Voltage PTC Air Heater Failure. This usually refers to internal breakage of resistive elements (PTC core) or open/short circuit at signal output terminals, preventing physical position and rotation speed information from being converted into effective electrical signals.
• Wiring and Connector Connection Abnormalities: Wiring Harness or Connector Failure. Involves communication paths between the sensor and control unit experiencing open circuits, loose connections, or corrosion, causing transmission link interruption.
• Controller Logic Judgment: The processing program inside the control unit failed to correctly identify the validity of the sensor signal, although belonging to the software category, it is typically associated with abnormal values at hardware signal input terminals in DTC classification.

Technical Monitoring and Trigger Logic

The generation of this DTC follows strict preset threshold monitoring algorithms, and its judgment mechanism is as follows:

• Monitoring Target: Real-time validity of temperature signal voltage/resistance values. System continuously checks if the physical quantity converted electrical signal from the passenger side PTC core surface has effective characteristics.
• Specific Condition: Fault trigger condition is set at ignition switch in ON position. System activates monitoring logic only during diagnostic cycles after ignition power is on, ensuring no false alarms occur when not powered.
• Judgment Threshold Logic: When the configured fault condition "unable to acquire temperature on passenger side PTC core surface" is met, if effective data streams or signal values cannot be obtained continuously or do not fall within preset valid physical ranges, the system executes fault lock and records B123F49.
• Time Window Requirements: Typically need multiple confirmations of signal loss within specific monitoring cycles to confirm permanent faults rather than instantaneous interference.