BMW Won’t Start After Accident | Replace BST Sensor
This guide will provide instructions on installing a BMW battery safety terminal kit, which you can order on eBay, and resetting the BMW airbag light, which comes on when the BST sensor fails.
BMW owners may experience their cars not starting after an accident. This problem is often caused by a fault in the BMW Battery Safety Terminal (BST sensor) mounted on the positive terminal.
BST sensor is often confused with the intelligent battery sensor (IBS), which is mounted on the negative terminal.
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Symptoms of bad BST
Symptoms of bad BST sensor include:
- BMW won’t start
- BMW will not start after an accident
- If airbags are deployed, BMW won’t start.
- Accessories and lights STILL work.
- The airbag light is on.
If you are stranded on the road and can’t start your BMW, check to ensure the battery’s positive cable is not loose. If it loses, the BST ignited and disconnected the positive.
How to Replace the BMW Battery Safety Sensor
What you will need
- BMW BST Sensor
- 10mm open-end wrench
- Flat Screwdriver
Procedure
- Park the BMW on level ground, turn off the ignition, and engage the parking brakes.
- Press the trunk release button and open the trunk.
- 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. The battery will be mounted on the trunk floor of a station wagon.
- Use a 10mm open-end wrench to disconnect the negative battery terminal.
Disconnect the positive battery terminal.
Remove the old BST sensor. First, unplug the airbag’s two black wires. Next, remove the 12mm nut that connects the accessory cable to the battery clamp. 
Install the BMW BST sensor. Connect the two wires for the airbag module, the positive battery terminal, and the negative terminal.
Locate the diagnostic port under the dashboard.
Connect any scanner that can read airbag fault codes.
Clear BMW fault codes are stored in the airbag module.
Remember that a basic code reader can not clear BMW airbag codes.
Bypassing BMW BST Sensor
CAUTION! This fix is not recommended.
If the BST sensor explodes (ignites), it should be replaced. Some BMW owners bypass the BST sensor by cutting the wires to it and installing a resistor. This allows you to clear the airbag light but disables a key safety feature.
Two small wires that go to the BST sensor (near the battery-positive terminal) are shorted with a resistor to bypass it. 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 the YOUCANIC Full System Scanner.
When you install a BMW BST bypass sensor, you remove a safety feature and increase the chances of a fire if you get involved in an accident. You can replace the sensor yourself.
In the past, replacing the BMW battery safety terminal would cost anywhere from $500 to $900. This is why some BMW owners bypass the BST sensor and connect the positive cable directly to the battery-positive terminal.
By deleting the BMW BST sensor, you will disable a safety feature on your BMW. Today, you can get a BMW BST repair kit, which you can order on eBay for a fraction of the original price.
Another solution is to remove the BST from a used BMW and install it on yours. However, you must ensure that the BST is not from a BMW involved in an accident.
Frequently Asked Questions
Where is the BMW battery sensor?
BST sensor mounts at the end of the battery-positive cable and is part of the battery-positive clamp that attaches to the battery post.
What does the BMW Battery Sensor do?
It is designed to disconnect the battery when the car is involved in an accident.
Which BMW models have an intelligent battery sensor?
BMW introduced the Battery Safety Terminal in the early 2000s.
Can I delete the battery sensor on a BMW?
Yes, but we don’t recommend deleting the BMW BST sensor. If you bypass the BST sensor and are involved in an accident, the battery will stay connected, increasing the chance of a fire or explosion caused by a battery shortage.
We hope you find the BMW Won’t Start After Accident | Replace BST Sensor guide helpful. Check these troubleshooting and repair guides for more help on your BMW.
HELLO, DO YOU KNOW WHERE CAN I BUY A CONNECTOR FOR THE POSITIVE CABLE, I HAVE A 328I AND MINE IS NOT THAT GOOD. MY BAGS DEPLOYED AND I PUT A NEW CABLE AND I REALIZE THE CONNECTOR IS NOT THAT GOOD. ALSO, DO YOU KNOW IF THE CONNECTOR IS NOT GOOD WILL THAT TRIGGER THE NEW BAG TO DEPLOY? IM THINKING TO WELD THE CONNECTOR TO THE ACTUAL CABLE BUT NOT SURE IF THAT WOULD WORK?