P1AF600 Power Battery Thermal Runaway Fault Technical Description

Detailed Fault Definition

Fault code P1AF600 is a critical diagnostic identifier involving high voltage safety in the Battery Management System (BMS), its core definition being "Power Battery Thermal Runaway Fault". At the electrical architecture level, this fault code indicates that the vehicle control unit has identified an unstable exothermic chemical reaction trend or actual thermal runaway event occurring within the power battery pack.

As the monitoring core for battery State of Health (SOH) and high voltage safety loop, triggering P1AF600 means the BMS determines the electrochemical reaction of the current battery pack has exceeded the passive safety protection threshold designed by the system. This fault plays the role of a Level 1 Safety Alert in the system, aiming to prevent high voltage safety accidents caused by chain reactions triggered by internal cell short circuits, hydrogen evolution or electrolyte decomposition. When this fault is activated, system logic forces the high voltage cut-off mechanism to intervene, preventing further energy release from causing irreversible harm to the vehicle and occupants.

Common Fault Symptoms

According to diagnostic database records, when P1AF600 fault code is in active or current status, the vehicle control unit will send specific signals to the instrument panel to warn the driver or enter a safety protection mode. Specific driving experience and feedback symptoms perceptible to car owners include but are not limited to:

• Instrument Display Abnormalities: The "High Voltage Battery" or "EV Powertrain" fault light on the dashboard lights up, accompanied by a thermal runaway specific warning icon.
• Limited Power Output: Due to the system determining a high-risk state, power commands received by the Motor Control Unit (MCU) are cut off; the vehicle may suddenly lose power or retain only very low torque creep capability to maintain safe parking.
• High Voltage Disconnection Protection: The battery relay (contactor) is forced open after fault detection, causing the entire vehicle high voltage system to not power on or charging to stop.
• Thermal Management Alert Linkage: If equipped with BMS and TCU thermal coupling logic, it may simultaneously trigger HVAC system shutdown to prevent heat accumulation.
• Vehicle Unable to Start/Shutdown: If severe thermal runaway signs are detected (e.g., sudden increase in temperature sensor readings), the system will prohibit high voltage loop closure, causing the vehicle to be unable to drive normally or shake hands when charging gun is plugged in.

Core Fault Cause Analysis

For this fault code, technical diagnosis must follow strict logic stratification, investigating from three dimensions: hardware physical state to software logic judgment. Blindly replacing equipment is prohibited before the fundamental physical mechanism is clarified.

• Power Battery Pack Hardware Component Abnormalities: This is the primary cause leading to P1AF600. Guided by original data "Power Battery Pack Fault", it specifically manifests as uncontrolled physical short circuits inside cells, direct contact between positive and negative electrodes caused by diaphragm rupture, or significantly increased self-discharge rates triggered by cell aging. Such hardware failures cause heat generation rate to exceed design redundancy of the cooling system, forming a positive feedback loop.
• Wiring and Connector Connection Abnormalities: Involving open or short circuits in lines for thermal runaway monitoring sensors (such as NTC temperature probes), which may lead the BMS to read false high-temperature signals. Although this belongs to false reporting, in fault logic judgment, if sensor feedback signal values exceed physical limit ranges, the system still needs to record it as "Battery Pack Fault" status to execute safety strategies.
• Controller (BMS/VCU) Logic Operation Judgment: The controller is responsible for real-time analysis of multi-channel sensor data streams. If control algorithms fail to correctly identify the difference between environmental temperature rise and exothermic chemical reactions, or if thermal management system logic judgment errors occur, fault codes may also be set.

Technical Monitoring & Trigger Logic

Triggering P1AF600 is not a single signal point, but a high dynamic safety strategy based on multi-parameter fusion in the Battery Management System (BMS). Its judgment logic mainly covers the following monitoring targets and conditions:

• Monitoring Targets:

  • Cell Temperature Distribution Consistency: The system collects BMS temperature sensor data for each module and level in real time, calculating the temperature difference ($\Delta T$) between adjacent cells.
  • Single Cell Voltage Differential: Under charging or discharging conditions, monitor drastic voltage fluctuations of single cells in a very short time (e.g., $V_{diff} > \text{threshold}$), judging whether internal short circuits exist.
  • Thermal Runaway Gas Pressure: Some high-order BMS systems will monitor air pressure changes inside the battery pack cavity to identify gas expansion trends produced by electrolyte decomposition.

• Trigger Logic & Conditions:

  • Faults are typically monitored primarily under dynamic operating conditions during motor operation or fast charging high-load conditions.
  • Judgment logic includes "exothermic rate" monitoring: when the heat generation power $P_{gen}$ inside battery unit exceeds the power $P_{diss}$ that the cooling system can remove, and temperature rise slope $\frac{dT}{dt}$ exceeds the threshold set by the safety model, the fault triggers immediately.
  • After the system enters this fault state, it will immediately cut off the high voltage main circuit contactor (HV Relay), isolating the power battery pack from the motor and charging interface, and activating passive safety strategies (such as releasing smoke detector signals).

• Numerical Range Explanations:

  • Specific temperature thresholds (e.g., $150\degree C$) and voltage differential thresholds belong to private calibration data of different vehicle BMS controllers and are not cited as general standards in technical diagnostic documents.
  • But generally, trigger logic follows physical safety boundaries, i.e., when monitoring parameters exceed the Thermal Runaway Critical Point, regardless of specific values, the system will immediately execute $HV_{Off}$ instructions.