BMW Not Starting Due to BST Sensor

A problem BMW owners may face is the car will not start after an accident. This problem is often caused by the BMW Battery Safety Terminal also known as BMW BST sensor or intelligent battery sensor.

BMW introduced the Battery Safety Terminal in the early 2000s. In this guide, we will show you how to install a BMW battery safety terminal kit and reset BMW airbag light yourself. Plus learn why you should not bypass or delete BMW BST sensor.

In this article.

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What is BMW Battery Safety Terminal?

BST sensor mounts at the end of battery positive cable and is part of the battery positive clamp that attaches on the battery post.

It is designed to disconnect the battery when the car is involved in an accident.

Symptoms of bad BST

Symptoms of bad BST sensor include:
  • BMW won't start
  • BMW will not start after accident
  • If airbags deployed BMW won't start
  • Accessories and lights STILL work
  • Airbag light is on 

If you are stranded on the road and can't start your BMW, check to make sure the positive cable at the battery is not loose. If it is lose it means the BST ignited and disconnected the positive. 

How to replace BMW BST Sensor

In the past, it would cost anywhere from $500 to $900 to replace BMW battery safety terminal. Which is why some BMW owners would delete BMW BST sensor and connect the positive cable directly to the battery positive terminal. 

By deleting BMW BST sensor you will be disabling a safety feature of your BMW. Today you can get a BMW BST repair kit for a fraction of the original prices. 

Another solution is to remove the BST from a used BMW and install it on yours. You need to make sure that the BST is not from a BMW that was involved in an accident

Step 1

BMW battery safety terminal is located where the battery is, which in most BMW is in the trunk. Start by opening the trunk.

how to change bmw bst sensor

Step 2

Remove the plastic retainers on the right side of the trunk. This will allow you to remove the right panel and access the battery safety terminal.

bmw battery safety terminal location

 Disconnect negative battery terminal. 

Step 3

Disconnect positive battery terminal.

disconnect bmw battery safety terminal

Step 4

Remove the old BST sensor. Unplug the two smaller wires that connect to the airbag module. Remove the 12mm nut that connects the accessory cable to the battery clamp. Next, you will need to disconnect and in some cases even cut part of the positive cable.

bmw bst kit installation

Install BMW BST repair kit. Throw away the old BST. Connect the new BST by following the instructions that came with the new BMW battery safety terminal kit. Rember to connect the two wires that go to the airbag module. 

Step 5

Connect positive battery terminal. The last step is to connect the negative terminal. 

bmw bst repair kit

Step 6

Clear BMW fault codes stored in the airbag module. For this step, you will need a scanner can read BMW specific fault codes such as Foxwell for BMW.

A generic OBD2 scanner can not clear BMW airbag codes. Choose a BMW scanner to perform this task. 

How is BST Sensor Bypassed 

 CAUTION! This method is not recommended. Perform it at your own risk. 

If the BST sensor exploded (ignited) it SHOULD be replaced. Some BMW owners decide to bypass the BST sensor by cutting the wires to the sensor and installing a resistor. This allows you to clear the airbag light but disables a key safety feature. 

To bypass the BST sensor two small wires that go to the BST sensor (near battery positive terminal) are shorted with a resistor. 

A 2-ohm resistor is installed at the end of the wires bypassing the BST sensor. This will emulate a working BMW sensor and the airbag light codes are reset using a BMW scanner. This solution is not recommended. 

bmw bst delete with 2 ohm resistor

It is not recommended to delete BMW BST sensor by installing a resistor. The cost of BMW BST repair kit currently runs for under $100,

When you install a BMW BST bypass sensor you are removing a safety feature and increasing the chances of fire in you get involved in an accident.  You can replace the sensor yourself. Use a scanner such as Carly for BMW or Foxwell for BMW to clear the airbag light once you replace BMW BST sensor. 

CAUTION

We do not recommend deleting BMW BST sensor. If you decide to bypass the BST sensor and you are involved in an accident, the battery will stay connected. Which increases the chance of a fire or explosion caused by a battery short. 

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