I have a Bmw 5 series E61 and if I open the tail gate the central locking no longer works unless you use the manual key. I had my mechanic look at it and he said I needed a new key fob  as the fob did not give off a signal.

However, around 12 hours later the central locking will work again, the fobs give off a signal and will be fine unless I open the tail gate. I am wondering what could be causing this. Perhaps a relay, or a sensor is causing a feedback to the key fobs which stops them working for a while? It will disable all the fobs nearby that unlock it.

Morning Paul

Welcome to the Forum

My bet would be the Diversity antenna has suffered water ingress (common at around your cars age) or the loom (left hand side) where the boot hinge is has a crack in one or more of the wires (less common). My money would be on the Diversity antenna try holding the key on top of the rear spoiler that sometimes works 

Remember if you change the antenna your keys will need to be re-programmed to the car. Use www.realoem.com to get the correct part number for your car then use Google to search for the part. If your antenna is not in to bad a state you could try repair specialists like Cartronix or ECU testing to see if they can fix it.

Changed a few of these including my brother inlaws 😁 

Good Luck 

Dave

GPS stopped working too, I presume this means it will more likely be the antenna than the wiring?

I would start with the Antenna get the Part Number from the one in the car or www.realoem.com and find a replacement 

Changing it will take around Half an Hour reprograming your Keys about 5 to 10 mins 

Or if your a real Tinkerer you could take the Antenna out open it up and see if you can fix it

Dave

bmw diversity antenna   serial number is 9183564-01. Not cheap to replace £150 second hand at lease. Anyone know where I can get one cheaper?

I would guess £500 + + from a Dealer so not exactly dear if yours isn't working 😁

Check www.reaoem.com either search by Vin number then through the sections or by the Part number you have. If you aren't aware double click the part number and you should get a list of alternates.

Then check the normal Auction sites but don't forget there is a healthy BMW Specialist dismantler network they may help

Dave