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Summary
  • BMS stands for “Battery Management System.” It’s the assembly that houses and keeps the batteries operational.
  • The BMS monitors battery levels, optimizes battery performance, and controls battery temperature.
  • A BMS reset restores the BMS to its default settings to make sure it works as intended.

Battery management systems for electric vehicles play a huge role in keeping EVs operational. They keep the batteries in good condition to maximize the vehicle’s performance.

But what exactly does this system do, how does it work, and what makes resetting it so important?

What Does “BMS” Stand For?

The BMS stands for “Battery Management System”. It’s an assembly that contains the batteries that power an electric vehicle and performs various functions to keep the battery operational, including the following:

  • Monitoring battery levels
  • Stabilizing batteries to prevent them from overheating
  • Protecting the battery from damage
  • Optimizing battery performance
  • Allocating battery power to different parts of the vehicle

Drivers need to pay close attention to the BMS because it tracks the overall state of health (SOC) of a battery.

The BMS uses sensors that monitor the current, voltage, temperature, and state of charge of the battery (SOC). Then, it adjusts and allocates how much charge the battery takes in and puts out based on its findings. It actively protects the battery against overcharging, deep discharge, overheating, and excessive current draw to prevent damage to the battery.

The system also sets the optimum range and parameters under which the battery should operate. The BMS checks to make sure all cells in a battery pack charge and discharge evenly and flags bad cells. The BMS controls the heating or cooling systems within the battery to keep it operating within its ideal temperature range.

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It also generates reports on the battery’s status and performance. Additionally, it can limit the vehicle’s power output or put the car in fail-safe mode to minimize risks if a fault is detected.

, What Is a BMS Reset? When and How to Do It

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: On an EV, the BMS acts as the battery pack’s “brain,” making decisions based on the data it collects to optimize performance and ensure safety.

Why Should You Reset the BMS?

battery management system bms of ev
Resetting the BMS is only necessary when the system malfunctions or the battery isn’t performing as usual.

Resetting the BMS restores the system to its default settings, allowing it to make adjustments to battery performance according to the vehicle. The reset helps extend a car battery’s lifespan by ensuring efficient power use.

A reset can also fix BMS issues because it clears the system’s data and reboots the sensors, allowing the BMS to gather data and start anew.

Resetting the BMS is only necessary when the system malfunctions or the battery isn’t performing as usual. It’s also a must if the BMS was recently installed to let it make the adjustments needed to optimize battery performance.

Non-electric vehicles don’t have complex battery management systems like those used on electric vehicles. However, newer non-EVs do have a basic system to manage the battery, so on a non-EV, a BMS reset might be necessary after a 12-volt battery replacement or a system malfunction.

Non-electric vehicles don’t have complex battery management systems like those used on electric vehicles. However, newer non-EVs do have a basic system to manage the battery, so on a non-EV, a BMS reset might be necessary after a 12-volt battery replacement or a system malfunction.

Richard McCuistian, ASE Certified Master Automobile Technician

Signs the BMS Needs to Be Reset

You might need to reset the BMS if the car battery drains quickly or overheats. Irregular charging patterns and frequent false alarms are also signs to watch out for.

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Batteries Drain Quickly

Batteries that can’t hold their charge well are either defective or being mismanaged by your vehicle’s BMS. That’s why a battery that empties quicker than usual might indicate the need for a reset. If the battery is very old it may need to be replaced. No battery lasts indefinitely.

Overheating Batteries

If a battery overheats due to a malfunctioning BMS, it runs the risk of exploding via thermal runaway. Not only can this permanently damage your vehicle, but it can also injure you and other people.

When the car battery overheats, it can affect engine performance and emit smoke and foul sulfuric smells. In some cases, it might even make hissing noises. If it catches fire, it’s almost impossible to extinguish, even for firefighters.

, What Is a BMS Reset? When and How to Do It

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Many EV batteries are liquid cooled, with heat exchangers (like radiators) and some have more than one coolant pump. Typically, EVs with air cooled batteries will have much lower performance requirements than high performance long range EVs.

Frequent False Alarms

The BMS manages the battery to ensure it operates within certain parameters using data from sensors that measure electronic activity and battery consumption.

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When these sensors detect that the battery is malfunctioning, they trigger an alarm to indicate that something is wrong.

A faulty BMS can trigger these alarms even when the battery works as intended. In this case, it’s a good idea to reset the BMS. It’ll recalibrate the system and its sensors, potentially stopping the BMS from making the same mistakes.

Inconsistent Battery Charging

If the voltage allocated to the battery when charging fluctuates drastically, resetting the BMS could stabilize it.

How to Reset the BMS (varies depending on the vehicle)

Every vehicle is different, so the steps to reset the BMS can vary. For more precise instructions for your vehicle, it’s best to check your owner’s manual.

Resetting the BMS usually involves the steps below.

  1. Fully charge your vehicle’s battery.
  2. Disconnect any chargers or power sources to ensure nothing is actively charging the battery.
  3. Remove the battery from the vehicle and let it settle for thirty minutes to an hour to dissipate residual electricity.
  4. Press and hold the reset button on your battery to reboot the battery and the BMS.
  5. Wait thirty minutes after resetting the BMS before reinstalling it on your vehicle.

If no reset button is available, you might need to bring your vehicle to a dealership or an auto shop. Professionals can examine your vehicle and reset the BMS if it’s necessary.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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