The battery safety terminal (BST) in your BMW E90 plays a crucial role in protecting you in the event of a collision. A faulty signal wire to the BST can trigger airbag system errors. This guide provides a detailed walkthrough for replacing the airbag signal wire connected to the BST in a BMW E90, specifically addressing an issue common in early models.
Understanding the Problem
Early model BMW E90s (e.g., 2006 330i) often experience intermittent airbag system errors due to a problem with the short signal wire running from the BST to the airbag wiring harness. While the BST itself is rarely the culprit, this 6-inch wire can develop internal issues leading to fault codes. Replacing this wire often resolves the problem.
Parts and Tools
- Replacement Airbag Signal Wire: BMW Part # 61129130178. This wire is significantly longer than the original but includes the correct connectors for the BST.
- Nose Pliers: For manipulating the BST’s plastic housing.
- Small Flathead Screwdriver or Pick: For disassembling the Takata connector.
Replacement Procedure
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Disconnect the Battery: Safety first! Disconnect the negative terminal of your battery before starting any work.
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Access the BST: Remove the battery and unbolt the BST’s battery cable from the rear wall of the battery compartment. This allows for easier access to the signal wire connection.
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Disconnect the Old Wire: The signal wire connector plugs into the BST at a 90-degree angle. The BST’s plastic housing may obstruct removal. Carefully use nose pliers to gently bend the flexible plastic portion of the housing near the connector. This creates enough space to disengage the connector’s locking tabs and pull it out.
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Connect the New Wire: The new wire’s connector should easily slide into the BST and click into place. Ensure the locking tabs are engaged. Gently bend the BST housing back to its original position.
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Prepare the Takata Connector: The new wire comes with bare wire ends. You’ll need to reuse the existing black/yellow Takata connector from the old wire. Carefully disassemble the Takata connector, noting the position of the wires (polarity may not matter, but it’s best to be consistent). Remove the old wires and insert the new wires into the corresponding slots, ensuring they are fully seated. Reassemble the Takata connector.
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Manage Excess Wire: The new wire is much longer than needed. You can either shorten it by cutting and soldering (recommended for a professional finish) or neatly bundle and secure the excess wire along the side of the battery compartment.
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Reassemble: Reinstall the BST, reconnect the battery cable, and reinstall the battery.
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Reset Airbag Module: After reconnecting the battery, you may need to reset the airbag module using a diagnostic tool.
Conclusion
Replacing the airbag signal wire on the BST of an early model BMW E90 can resolve frustrating intermittent airbag system errors. While the process requires careful manipulation of the BST housing and the Takata connector, it’s achievable with basic tools and patience. Following these steps will help ensure a safe and properly functioning airbag system.
