1. Power Supply:
* Battery Voltage: A weak battery can cause intermittent or complete failures of electrical components. Test the battery voltage with a multimeter. It should be around 12.6V when the car is off and slightly higher when running.
* Battery Terminals: Check for corrosion or loose connections on the battery terminals. Clean them thoroughly if necessary.
* Alternator: A failing alternator can't keep the battery charged, leading to similar symptoms. Have the alternator tested.
2. Wiring and Connectors:
* Comfort Module (or similar): BMWs often have a central control module for seat and steering wheel adjustments. This is a likely culprit. This module is usually located under the driver's seat or in the center console. Inspect its connectors for corrosion, loose connections, or damaged wires. This requires removing some interior panels, so consult a repair manual.
* Wiring Harness: Examine the wiring harness running from the comfort module to the steering column and seat for any visible damage (cuts, fraying, etc.). This can be tricky to access.
* Ground Connections: Poor ground connections can disrupt electrical signals. Check all ground points related to the seat and steering column.
3. Control Module (Comfort Module or similar):
* Diagnostics: The most likely scenario is a faulty control module. You'll need a BMW-specific diagnostic tool (like INPA, ISTA, or a compatible OBD-II scanner) to read fault codes from the vehicle's modules. This will pinpoint the exact problem. A professional mechanic will have these tools.
* Replacement: If the diagnostic tool points to a faulty comfort module (or similar), it will likely need to be replaced. This is usually a costly repair.
4. Less Likely but Possible Issues:
* Steering Column Switch: While less likely given both seat and steering wheel are affected, a problem within the steering column switch itself *could* impact both, although this would usually manifest differently.
* Short Circuit: A short circuit somewhere in the related wiring could disrupt power. This is difficult to diagnose without a proper diagnostic scan.
Important Considerations:
* Repair Manual: Accessing and working on these systems requires careful attention to detail. A repair manual specific to your BMW model is strongly recommended.
* Professional Help: Unless you have significant experience with automotive electrical systems, it's best to take your car to a qualified BMW mechanic or a reputable auto electrician. Improper diagnosis or repair can lead to further damage. The diagnostic scan alone is often worth the cost of professional help.
Starting with the simple checks (battery, fuses, connections) is a good first step, but the simultaneous failure of both systems points to a more complex electrical problem within the vehicle's control systems. Professional diagnostics are highly recommended.
