Central locking gremlin ‘95 M3

[chambolle]

Please forgive me if this is a bonehead question; but here goes. I am original owner of a ‘95 M3; it was my daily driver for two decades but has been driven little since I bought an M2 in late 2016. I keep it spic and span and garaged; and drive it when the sun shines... which in the Pacific Northwest ain’t all that often.

There is a ‘professionally installed’ small powered subwoofer in the trunk. To avoid possible battery drain, I switch the subwoofer power off unless I intend to use the sound system (original head and trunk-mount cd changer, upgraded speakers and underseat amp).

I noticed today the central locking system was not working. Fuses fine; but I had a wild idea — is the subwoofer powered off? It was, so I flipped the switch on the subwoofer case (it’s a little flat Alpine unit). I mean why not? I had no better plan.

I’ll be damned... the central locking system works just fine now.

After reading various posts addressing locking system issues, I didn’t see anything addressing this bizarre quirk. Any idea what the installer may have done that could explain this phenomenon; and if there’s an easy fix, what might that be?

[Eric93se]

I don't think they are related. If you haven't already done so I would put a float charger on the battery. Get one that can turn itself on/off automatically.

[xxxxxxx]

You've tried it several times and replicated the results? Or just once?

[bluptgm3]

Central locking issues can be caused by a break in the trunk wire loom just as it goes into the trunk lid.


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[chambolle]

I don't think they are related. If you haven't already done so I would put a float charger on the battery. Get one that can turn itself on/off automatically.

I have one of those BMW branded trickle chargers and put the car on it for 48 hours or so, once or twice a week. Unfortunately I don’t have access to AC in the garage where the car is usually stored, so that’s the best I can do; but it has been successful at keeping the battery topped up.

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You've tried it several times and replicated the results? Or just once?

Actually only tried it once; and you're right... ‘temporal contiguity is not causation.’ I’ll have to repeat the experiment a number of times.

[chambolle]

[QUOTE=bluptgm3;30684581]Central locking issues can be caused by a break in the trunk wire loom just as it goes into the trunk lid.


Which makes sense... the subwoofer is likely hitched to the bundle of wires that runs from the dashmount radio head unit to the back end of the car. And to complicate matters, I had a family of mice who took up residence in the trunk last winter; who knows what they chewed (or pissed on).

[JDStrickland]

Please forgive me if this is a bonehead question; but here goes. I am original owner of a ‘95 M3; it was my daily driver for two decades but has been driven little since I bought an M2 in late 2016. I keep it spic and span and garaged; and drive it when the sun shines... which in the Pacific Northwest ain’t all that often.

There is a ‘professionally installed’ small powered subwoofer in the trunk. To avoid possible battery drain, I switch the subwoofer power off unless I intend to use the sound system (original head and trunk-mount cd changer, upgraded speakers and underseat amp).

I noticed today the central locking system was not working. Fuses fine; but I had a wild idea — is the subwoofer powered off? It was, so I flipped the switch on the subwoofer case (it’s a little flat Alpine unit). I mean why not? I had no better plan.

I’ll be damned... the central locking system works just fine now.

After reading various posts addressing locking system issues, I didn’t see anything addressing this bizarre quirk. Any idea what the installer may have done that could explain this phenomenon; and if there’s an easy fix, what might that be?

"... in the trunk."

Since you open the trunk by pushing a button (because you car does not have an an electric trunk latch) then my money is on the idea that you have a broken wire or two in the harness from the left fender to the trunk lid. You open and close the trunk and the symptoms changed (they were cured). There is a large grommet where the harness goes into the trunk lid, pull then back and push it down toward the fender to expose the wires. If you need to make repairs, it helps a lot to remove the liner from the trunk lid, this lets you push and pull the wires as needed to splice in new sections. When my car was giving me fits with the broken wires, I was able to manipulate the wire harness while the trunk lid was open and change the symptoms on the fly.

[JDStrickland]

[QUOTE=chambolle;30684750]

Central locking issues can be caused by a break in the trunk wire loom just as it goes into the trunk lid.


Which makes sense... the subwoofer is likely hitched to the bundle of wires that runs from the dashmount radio head unit to the back end of the car. And to complicate matters, I had a family of mice who took up residence in the trunk last winter; who knows what they chewed (or pissed on).

I would caution you that the issues with the locking and the issues with the sound system are unrelated. I could be wrong, but I would go into this thinking that the central locking system was on the fritz, not that the sound system was bad. The sound system does not share the wires that go from the fender into the trunk lid, but the locking system absolutely does go into the trunk lid. You can lock the trunk using the central lock system, and you can use the key in the trunk to unlock the car or lock the car, but not both and I forget which way it goes. My car would either lock or unlock the car from the trunk latch, but when the trunk latch was in the vertical position, the trunk would both lock and unlock from the central locking system.

[chambolle]

[QUOTE=JDStrickland;30684779]

I would caution you that the issues with the locking and the issues with the sound system are unrelated. I could be wrong, but I would go into this thinking that the central locking system was on the fritz, not that the sound system was bad. The sound system does not share the wires that go from the fender into the trunk lid, but the locking system absolutely does go into the trunk lid. You can lock the trunk using the central lock system, and you can use the key in the trunk to unlock the car or lock the car, but not both and I forget which way it goes. My car would either lock or unlock the car from the trunk latch, but when the trunk latch was in the vertical position, the trunk would both lock and unlock from the central locking system.

Well sure enough, it seems the putative relationship between the subwoofer and the locking system was purely coincidental and spurious. I could not replicate the subwoofer off/locking system on phenomenon. But the locks all work in tandem again.

There must be some funky wiring in the trunk lid that intermittently connects and disconnects; that’ll be more than fun to track down I’m sure.

And to prove that Roseanne Rosanadana was right — ‘it’s always something’ — today I noticed a little puddle of bluish fluid (coolant, of course) forming on the concrete below the front end. Which is disheartening given I had the water pump, radiator, hoses, expansion tank all replaced and upgraded (aluminum radiator, silicone hoses, Stewart stainless steel pump) just a few years ago.

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And thanks to everyone for your advice; and for bearing with my clueless inquiry!