P15794B Inductor Temperature High: Fault Definition and Technical Analysis

### Fault Detailed Definition

Diagnostic Code P15794B (Inductor Temperature High) is a critical thermal protection diagnostic indicator in the vehicle power supply system. In the automotive electrical architecture, inductor components are typically located within the On-Board Power Supply Assembly, performing essential physical roles such as energy storage, filtering, and energy conversion. This diagnostic code indicates that the system monitoring unit has detected that the actual operating temperature of the inductor component has significantly exceeded the preset safe operating threshold.

This fault is not merely a simple sensor reading anomaly; it directly points to an On-Board Power Supply Assembly Internal Fault. From the perspectives of thermodynamics and control logic, uncontrolled inductor temperatures may imply that the balance between internal heat generation rate (Power Dissipation) and heat dissipation rate has been disrupted. The core purpose of diagnosing this code is to confirm whether the physical component's thermal tolerance has decreased or if the system control strategy triggered an overheat protection mechanism to prevent electrical short circuits or insulation failure risks caused by high temperatures.

### Common Fault Symptoms

When P15794B diagnostic code activates, the vehicle control system will enter corresponding safety modes according to diagnostic logic, and vehicle owners may perceive the following abnormal phenomena during driving:

• Instrument Panel Indicator Alarm: The status indicator light for the On-Board Power Supply Assembly or a generic power source warning light illuminates on the dashboard, indicating to the driver that the system has a thermal fault.
• Power Supply Performance Degradation: Due to the intervention of protection logic, the On-Board Power Supply Assembly may limit maximum output current, causing electronic devices relying on this power supply to experience voltage fluctuations or sluggish response.
• Intermittent Functional Failure: Some onboard systems requiring stable DC bus voltage may exhibit sporadic restarts or functional interruptions, manifesting as unstable operation of windows, dashboard backlights, or other electric modules.
• Engine/Motor Control Restriction: In hybrid or electric vehicles, if the inductor serves a drive circuit or auxiliary inverter, high temperatures may trigger power system torque reduction protection or power limitation strategies.

### Core Fault Cause Analysis

Addressing the fundamental judgment of On-Board Power Supply Assembly Internal Fault, from the technical principle perspective, specific factors leading to excessive inductor temperature can be summarized into the following three dimensions:

• Hardware Component Aging and Damage: Insulation material around the inductor coil windings may undergo thermal aging due to long-term high-temperature environments, leading to decreased insulation resistance. Additionally, if the saturation characteristics of the inductor core change, or losses increase in high-frequency switching applications, internal heat generation will rise sharply. Under extreme conditions, internal shorts may produce local hotspots with temperatures exceeding safety thresholds.

• Wiring and Cooling Path Abnormalities (Physical Connection Dimension): Although the fault points to the assembly interior, internal connector contact resistance must be considered. If connection points between internal inductors and power rails within the assembly oxidize or loosen, additional contact thermal resistance will be generated. Simultaneously, if passive heat sinks inside the assembly accumulate dust, thermal interface glue detaches, or cooling air ducts are blocked, heat cannot dissipate to external air in time, causing locally high temperature accumulation.

• Controller Logic Computation Deviation: The control unit of the On-Board Power Supply Assembly is responsible for real-time calculation of the inductor's thermal state. If a temperature sensor (such as a thermistor) integrated near the inductor drifts, opens, or outputs abnormal signals, it may cause the controller to misjudge the actual temperature as high. Additionally, if protection algorithm parameters within the controller are overly sensitive due to software updates or calibration errors, fault codes may be triggered even without overheating conditions.

### Technical Monitoring and Trigger Logic

The ECU (Electronic Control Unit) of the vehicle power supply system monitors inductor temperature through real-time feedback loops, with its determination logic primarily following the following principles:

• Monitoring Target: The system continuously collects surface temperature signals from the inductor winding and core area. This sensor is typically connected to the On-Board Power Supply Assembly's diagnostic interface in a differential form to isolate common mode interference and obtain precise local thermal field data. Monitoring content covers real-time voltage, current, and corresponding Joule heat loss calculation, estimating core temperature through physical models.

• Value Range and Threshold Determination: Although specific trigger temperatures depend on manufacturer safety calibration, system logic requires maintaining the inductor component within the temperature rise range allowed by insulation materials. Once measured or calculated temperature values exceed $T_{threshold}$ (preset safety threshold), the system will immediately record the event. This logic is typically executed under conditions such as drive motor operation, sudden load increase, or idling for extended periods for dynamic monitoring.

• Fault Determination Mechanism: A single sampling exceeding the limit does not trigger; the system will filter based on a certain duration (e.g., mean temperature within continuous $N$ scanning cycles higher than threshold). Once this time window condition is met, the controller marks DTC P15794B and stores diagnostic data in the fault memory. This delayed triggering mechanism aims to distinguish between transient spikes and sustained overheating states, ensuring fault determination accuracy and preventing false reports due to instantaneous load fluctuations.