Problems With the Battery Safety Terminal in BMWs

Posted on: April 13, 2019

As a BMW owner, you might try to start your car after an accident, even a minor one such as hitting a small object or going up and over a curb, only to find that the car isn’t starting. The reason for this is likely the battery safety terminal.

How would you know if you’re having trouble with your BST? Well, there are some telltale symptoms of a BST sensor problem, all of which will be noticeable after an accident. Symptoms of a problem with your BST sensor start with your BMW not starting, and especially your BMW not starting after an accident. If your airbags deployed because of an accident, your BMW will not start. However, you might notice that the airbag light is on and all of your accessories and other lights still work.


The Role of the BST


The battery safety terminal, otherwise known as BST, is used to reduce the risk of a short circuit to the B+ terminal of the battery in the event that a BMW is involved in an accident. The battery safety terminal helps to protect a short circuit the results of a short circuit on the cable that runs to the B+ terminal. This B+ terminal is part of the battery that connects to the starter and the alternator which means it is an unfused and unprotected circuit.


This is not a component that you would regularly have issue with unless you were involved in an accident. Depending on the severity of the accident, the MRS control module may send a signal to the BST telling it to disconnect the B+ cable that goes to the starter and the alternator.  That is why you might get a signal to your BST to disconnect your B+ cable after a major accident or after what seemed like an inconsequential accidental jump over the curb. Things that may not have been dangerous car accidents might still trigger that sensor.


If the BST is activated, then the power is supplied to the rear power distribution box, which is a fuse and protected power distributor. By moving power here, it allows the vehicle to activate other systems, such as power windows, power locks, hazard lights, and engine electronics, which is why the car won’t start but the interior lights still work.


On these vehicles, the battery cables are divided in the rear distribution box, so the remainder of the electrical system in your vehicle will remain operational if these safety battery terminal gets triggered. Of course, this is only going to happen if none of the other main fuses disconnected the circuits because of a short circuit resulting from a car accident.


Why does this matter so much?


Technical explanations aside, it is clear that this particular component plays a very important role in your long-term safety. Even though no one wants to consider being in a car accident, in the event that you are, you want certain functions to remain operational if at all possible, such as your hazard warning flashers or the ability to roll down the windows to call for help or open the doors. If this feature stops working properly and you don’t get it checked, the next time you are involved in an accident you might not be able to turn on your hazard lights to alert other people to the issue. You might not be able to use telephone function or open the doors to get out of the car.


Getting Repairs


If you’re having problems with your battery safety terminal, you can bring your vehicle into a professional auto mechanic who is certified to work on BMW’s. They can verify the issue, locate the source, and repair the problem before you ever need to make use of the feature. The replacement cost of a BMW BST sensor is a few hundred dollars, depending on where you go. You can have a certified mechanic use a repair kit, which is a fraction of the cost, to replace the entire terminal. A repair kit can help you save money after an accident and get your car back on the road.


BMW Battery Safety Terminal Issue Check


If you have any questions about your BMW or you are having additional problems with the battery safety terminal, reach out and get help today. You can contact our team of knowledgeable experts at European Auto Service Center Inc. We have three locations for your convenience, including our Aventura/Miami and Boca Raton East and West locations.

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