Reverse sensors work on and off

Should try a reset for the computer read about it in tour Manual First but I have seen this before

Go under the car and clean them.

No.
The speed sensor just measures road speed.
Is the check engine light on ?

put car into reverse with ignition on (not running) and either listen very closely or feel each sensor with your finger tips, you should hear a clicking noise or feel a ticking on the good sensors. once you have determined the faulty one simply release the two plastic retaining clips and push the sensor through the bumper inwards, then remove plug and fit new sensor

dear friend-before you even look at the gearbox,have a look at the TPS sensor,as this sensor acts on information from various other sensors and can affect
the gear changing pattern to its information.

I had the same problem on my 330d M-Sport Touring. My problem was identified as 2 faulty injectors al;lowing too much fuel to flow back into the fuel lines. This resulted in reduced common rail pressure and the ECU would not start the injectors. I recommend getting a leak back test done and this will confirm if the injectors are good or bad. Try and find a Bosch service centre as these guys will know how to do the test and also how to fit the injectors properly.
Good luck

I believe this is a safety feature of BMW I experienced the same thing on the 06 325

sounds like it could just be the reverse sensor located on the acctual gearbox under bonnet, you can tell which one it is as it is one of possible two.

leaking turbo hose? losing turbo presure thus the loss in power and the sound you here being turbo presure being lost through the bad pipe

As regards the auto lights. Just flick the sidelights on twice in quick succession and they should work. The reverse to cancel them. Can't say about the reversing sensors......best o luck. DK.