P15FF00 - P15FF00 Internal Temperature Sensor Fault

In-depth Analysis of P15FF00 Internal Temperature Sensor Failure

Deep Definition of Failure

P15FF00 is a key diagnostic trouble code (DTC) related to high-voltage power management in the control system of electric and hybrid vehicles, primarily associated with the thermal management system of the On-Board Charger (OBC). In the vehicle electrical architecture, the on-board charger is responsible for converting external AC grid energy to DC to charge the traction battery or, in certain configurations, supporting Vehicle-to-Load (V2L) discharge. The core logic of this fault code lies in the malfunction of the internal temperature sensor, indicating that the control unit cannot obtain accurate body temperature data of the on-board charger or detects an internal physical state exceeding safety limits.

As a key part of the vehicle thermal management strategy, the internal temperature monitoring mechanism of the on-board charger aims to prevent power device overheating, insulation material aging, and electrical short circuit risks. The triggering of P15FF00 means that the control unit of the On-Board Charger (OBC) judges that its internal temperature sensing circuit has abnormal signals or actual thermal state exceeds preset safety boundaries. This fault is directly linked to the passive safety logic of the high-voltage system and belongs to a warning signal of critical hardware health status, aiming to avoid continued operation near the thermal runaway critical point and prevent potential high-voltage fire or battery damage risks.

Common Fault Symptoms

When the on-board charger (OBC) internal control unit generates P15FF00 fault code, the vehicle's high-voltage electrical system will execute protective cut-off strategies, and drivers can perceive the following specific phenomena:

• Charging function completely restricted: After the vehicle enters AC charging status, the charging interface indicator light goes out or shows abnormality, the charging process is forcibly interrupted, resulting in inability to complete energy replenishment.
• V2L/External Discharge Function Disabled: If the vehicle has Vehicle-to-Load discharge function, the system will immediately close external power supply output after detecting the fault code, preventing load-side equipment overheating.
• Instrument Panel Fault Alert: The On-Board Information System (BCM or instrument control unit) may pop up text warnings such as "Charging Fault" or "High Voltage System Abnormality" on the central screen or multimedia screen, and may be accompanied by battery icon flashing.
• Automatic Restart Protection: In some working conditions, the on-board charger may attempt to reset logic to verify status, but once the temperature signal exceeds the limit again, it will repeatedly trigger charging prohibition instructions.

Core Fault Cause Analysis

Based on the definition of "On-Board Charger Internal Failure" in the original fault code data, this problem can be logically attributed to the following three technical dimensions:

• Hardware Component Dimension: The root cause of this dimension lies in the physical component failure inside the on-board charger module. Specifically includes internal temperature sensors (such as NTC thermistors) integrated on the OBC PCB board appearing open or short-circuited, resulting in inability to feedback effective resistance value; or power semiconductors (such as IGBT/MOSFET) near sensor packaging occurring overheating damage, although the sensor itself may be normal, but the collected environmental thermal signal is distorted.
• Line and Connector Dimension: Although the fault points internally, in technical diagnostic logic it needs to consider the integrity of the sensor signal line. High/Low temperature difference areas inside the on-board charger may cause the wiring connected to the sensor to appear with excessive contact impedance or damaged insulation layer, thereby making the controller read voltage values drift, unable to truly reflect the OBC internal thermal environment.
• Controller and Logic Dimension: The control unit (MCU) of the on-board charger may exhibit judgment deviation when executing algorithms. This includes abnormal filtering of analog signal signals collected from the sensor, failure to correctly identify fault trigger conditions, or errors in mapping relationship regarding "specified thresholds" in software calibration, leading to early triggering of protection logic before reaching actual dangerous temperatures, or failing to report status normally at critical points.

Technical Monitoring and Trigger Logic

The determination of P15FF00 fault code strictly follows the real-time thermal management strategy implemented by the on-board charger control unit, its monitoring process includes the following key technical nodes:

• Monitoring Target: The system continuously monitors temperature sensor signals in key heat dissipation areas or internal core elements of the on-board charger module. The core variable monitored is the difference relationship between the real-time collected temperature value ($T_{sensor}$) and the preset safe protection temperature parameters.
• Numerical Range Determination: Fault trigger logic is based on whether the real-time monitored temperature data breaks through safety thresholds. When $T_{sensor} > T_{threshold}$ (where $T_{threshold}$ is specified threshold), the judgment signal is considered exceeded. This judgment is only valid when the on-board charger is in an activated state, meaning it must be combined with operating conditions for comprehensive evaluation.
• Specific Operating Condition Trigger Conditions: Monitoring is not done when the vehicle is stationary or the charger is sleeping. The necessary environmental condition for fault code generation is Vehicle AC Charging or Discharge State. Only in these two high-power output/input operating modes will significant heat accumulation effects occur inside the on-board charger. When the control unit detects temperature exceeding specified thresholds under these dynamic conditions, it immediately generates fault code P15FF00 and executes system protection strategies.