Central brake light & boot lock problem

[MarkBevan]

Hiya,

I'm pretty uninformed on Z4's, having only had mine since Feb. Any advice from you experts, on this new (to me) issue ?

Last night I noticed that the far right bulb on the central brake light (on the boot lid) was on, even though the car was parked & there was no key in the ignition !

If I start the car and try the brakes, the central brake light comes on OK, but on releasing the brakes, the far right bulb still stays on.

Sometimes I'm getting the boot open warning light, when it isn't.

Sometimes when I press the brake pedal, I can hear the boot lock close motor firing.

If I open the boot using the BMW logo 'handle' on the boot, whilst I'm pulling the handle, that far right bulb goes off.

Any advice would be appreciated (confused of Enfield) !

[B21]

Sounds like a bad earth somewhere and/or the rear boot light connector has some corrosion in it..problematic chasing those faults...

Of course you don't have decent BMW specific fault code reader?

[Spriteracer]

Not sure if this is the case with the E89, but on several BMs I've had, these symptoms are very like ones which turned out to be caused by broken wires that had fatigue where they go through the boot or tailgate hinge. The wire breaks and the insulation hardens and flakes off allowing shorts between wires in the loom. I had it on E34 E39 and E61 and I know of another person with it on an old 7 series. Quite common on BMWs I think and causes issues with central locking, lights and rear wipers etc. I fixed all mine with soldered joints and heat shrink sleeves - there is not enough room in the wire bundle for more flexible connectors. It is a bit of a fiddle to do but quite possible DIY.

[MarkBevan]

Thanks for the suggestions guys

I don't have a decent BMW specific fault code reader yet (or any code reader).

As you say, it sounds like an earthing / wiring / connector corrosion problem

I had to repair the wiring that went through to the boot lid on my E39, as years of the wires flexing every time the boot was opened, eventually took it's toll

[RobbiZ4]

Thanks for the suggestions guys

Have a look at the maintenance thread...
viewtopic.php?p=1861524&hilit=brake+light#p1861524


... and look for brake light:
Update 03/2022:
There might happen a tricky fault on the boot lid: if the brake light gets activated, the trunk lid opens while driving.
Have a look at the following description:
[Deleted]viewtopic.php?p=1909115#p1909115
viewtopic.php?p=1725032#p1725032
This blue plug of the trunk lid harness can be found on the right next to the backlight cluster.

It might be a corroded blue plug in the trunk. Can be checked without tools and code readers. Juste remove the interior trim on the back.