1,000,000th Locking Post

All,
94 525i
My fuel door mechanism will unlock, but won't lock.
When I disassemble it, true to form, the motor only spins when I unlock.
Does this mean the circuit isn't reversing polarity properly? If so,
how does one test that?
Thanks! a.
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A DVM set to 20 volts across the line will show up a fault. It will read approx 12 volts when you lock and -12 volts when you unlock, or vice versa. If it does, the fault is in the motor. If not, in the controller. Alternately unplug and apply 12 volts from an external source. One of those cheap jump start packs is very handy for this sort of thing. If it runs in both directions when you reverse the polarity the motor is ok. If it's a simple two wire system this rules out a wiring fault to the motor so it must be either the controller or the control circuit operating it.
--
*A cubicle is just a padded cell without a door.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

Thanks Dave.
I'll give that a try today.
a.
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wrote:

So, I get approximately 12 volts when I press unlock, but nothing when I press the lock.
I can only assume the fun begins now.
a.
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I've a feeling on some models this motor is in parallel with the boot locking motor, so if this works ok it sounds like a wiring fault.
--
*I didn't drive my husband crazy -- I flew him there -- it was faster

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

I did a quick test last night...the boot (we call 'em trunks) lock works properly.
I'll see if I can follow that thing back to whereever it goes. Maybe I'll just buy one of my EE friends a beer.
a.
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If it does follow the 'trunk' motor - and that's shown on one BMW wiring diagram of the period I have - I'd first look at the wiring round the trunk hinge as the flexing can cause it to break. That does of course assume the pickup point for the flap motor circuit is at the actual trunk motor connector and not elsewhere.
Fixing this sort of fault requires good knowledge of the actual model as wiring diagrams often don't help with the location of connectors etc. And it's not unknown for the loom layout to alter during a model's life if problems arise. Or that's my excuse if I've lead you up a blind alley. ;-)
--
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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