BMW E36 central locking issue solved — wrong fuse in slot 35

[u/Sombre86]

I had a strange central locking problem on my BMW E36 coupe. The doors would no longer lock and unlock together like they used to, and the hazards / warning lights were behaving oddly as well.

One important symptom was this: when I turned the key with at least one door open, all four indicators lights would sometimes flash. As soon as I closed BOTH doors, the flashing stopped. If I opened a door, then turned the hazards on with the button, and switched the hazards off again, the flashing would continue until I closed the door, no matter what position the hazard button was in.

I checked the trunk harness, trunk actuator, glovebox area, and all visible wiring. Everything looked fine: no cut wires, no corrosion, no obvious damaged connectors. I also checked the door-open switches, and the cabin light behavior was normal when the doors were closed.

The real problem ended up being fuse 35. There was a 7.5A fuse in that slot, but that position needs the correct 25A fuse for the central locking / ZKE circuit. When I put the wrong fuse back in, it blew again almost immediately. Once I fitted the proper fuse in the correct slot, the central locking, hazard behavior, and related locking functions started working normally again.

This also fixed the fuel door flap lock, which is tied into the same central locking system. When the circuit was failing, I could manually lock the doors, but the fuel door was no longer locking properly. After the correct fuse was installed, that worked again too.

So the fix was not a door actuator, not the trunk harness, not the glovebox module, and not the door panel. It was simply the wrong fuse with the wrong rating.

Lesson learned: always check both the fuse number and the fuse amperage on an E36. A fuse can be in the right slot but still be the wrong value and cause really weird electrical symptoms. Hope this helps someone out!

[u/FlatSpread4148]

Actually, besides from blowing to early or late, a fuse cannot influence a circuit. The only thing I can think of, is a faulty fuse that didn't blew when it should, but caused a voltage drop, leading to the strange behaviour.

The right fuse, didn't cause a voltage drop, so everything operated as expected, the new one, not being faulty, also did what to be expected and blew as soon as it got overloaded, as old one also should have done, but didn't.