Immobiliser not allowing me to start rthe ca - 2005 BMW 1 Series

The immobiliser works with a chip in the fob. This is a signalling device which, via a pick-up situated around the ignition lock, sends the signal to the engine computor which the allows the engine to be started.

Often, you need to press the unlock button on the remote twice. First press unlocks the door and second press disables the immobiliser and allows the vehicle to start. The key alone will not start the vehicle.

Alternatively, when the key is in the ignition - press the remote unlock again.

The remote acts as an immobiliser device. The reason your car won't start on the key is probably because the system won't allow any key in the ignition - it is preventing theft of the vehicle. Once the unlock button on the remote is pressed the system then recognises that key is the legitimate one for the vehicle and the disables the immobiliser and allows you to start the car

the ECM and the CPU program do not recognize that you have passed the immobiliser so are not allowing the car to start. It is reading it as a key that is not suited to the system

replacing the battery energises the immobiliser so it will not allow the engine tom start. Try using a scanner to reset the immobiliser

There is a manual override switch inside the car that can turn it off.
Consult the alarm/immobiliser fitment centre for exact details.

the immobiliser is just one of several items that will not allow the car to start. The immobiliser has to recognise the key for it to work so if the key battery is flat it will not start. run fault codes to check cam./crank position sensor.

Very common story, your electrical system took a shook and has forgotten its memory, that means it thinks that it is stolen, no shortcuts sorry, it has to go to a dealer, if you ring them they may be able to come to you
Merry Christmas

I would be checking for a loose battery terminal ( from the bump) or a damaged battery. The immobiliser normally will not allow spark and normally does not stop the cranking action of the engine. If it is an auto a broken isolator switch for the park/ neutral position will also causes the fault

have you tried a code reader ?

Unfortunately there is no way to bypass the immobiliser on this vehicle, the immobiliser communicates with the control unit which then send s a start signal to the ECM to start the car, There are companies in the UK that can re-program the ecm to ignore the immobiliser but this isn't very cheap. You best option is to try to find a car at a dismantlers and replace the damaged part yourself.