Why Resetting Tesla BMS A079 Error Is Extremely Dangerous

Recently, there have been cases where some users continue operating their systems after an error code appears by performing a reset on BMS A079. However, this is an extremely dangerous act from the perspective of battery safety.

The most common causes of battery pack fires can be broadly divided into three categories:

1. Cell Degradation and Internal Short

   • Micro-shorts may occur inside the cell.

   • Although this may initially result in minor heating, if it continues, it can escalate into thermal runaway, spreading to the entire pack.

2. External Short

   • This occurs when wiring, connectors, or external circuits experience a short.

   • In my own experience, such incidents are frequently observed even during development and testing phases, and the fire risk is very high.

3. Loose Connection at Cell Joints (Loose Connection / Arc Fault)

   • Poor cell tab welding or improper busbar fastening can increase contact resistance, leading to localized heating.

   • If the current is momentarily interrupted and then reconnected, an arc may occur, causing insulation breakdown and sparks, which can escalate into an arc fire.

   • In my experience, this type of issue is also frequently observed during development and testing. Due to these risks, many large cell manufacturers refuse to supply cells to small and medium-sized enterprises.

     
     

Typically, cases such as (1) internal short and (3) loose connections can be detected by the BMS as similar anomalies, and in such cases, the BMS will issue a critical error code.

Since the BMS is developed in compliance with the highest levels of functional safety (ISO 26262 standards), the probability of false positives (errors that could cause harm to people or property without real faults) is extremely low. Therefore, when the BMS issues a critical error code, it is a strong indication that an actual fault compromising the pack’s safety exists.

Nevertheless, ignoring such warnings and simply resetting the system to continue operation is equivalent to disabling the BMS’s cell/pack protection functions. This is an extremely dangerous action that dramatically increases the likelihood of a fire in the event of an incident.