troubleshooting power door lock actuators

[JHZR2]

My 91 BMW 318i has very irregular operating power lock actuators in the front doors (rear doors are disconnected as one got stuck and the other stopped working).

They always lock, so they always work in the downward position, but they are very intermittent in the up position. I hear the lock relay click when I send the unlock signal, just nothing happens. Of course they lock and the relay clicks and all is well for that.

Im thinking that one isnt working and as a result, they all dont go. Like as if the resistance is too high so the circuit does not energyize or something...

Any ideas?

 

[Colt45ws]

My thought it, even if one goes out the others should still work fine. You can probably just unplug one to test this. Its likely using the same wires and just reversing the voltage depending on which way you are wanting it to go. Im going to guess it has something to do with the unlock relay or related circuity.
Though I have no BMW experience so this is just a best guess.

 

[JHZR2]

My only known issues are that one (passenger side) got stuck in the down position for a few days once, and that they seem to work more consistently when it is warm...

 

[fdcg27]

I didn't realize that you had a four door 318i.
Anyway, have you tried giving everything a good cleaning?
How much dust and grime might there be on these old mechanisms?
Also, how much resistance may have built up in the connectors as a result of years of minor tarnish and corrosion?
Finally, could the solenoids have simply become flaky through years of use?
A solenoid is, after all, just a linear electric motor.
Both door locks on my old 318 still work fine, but their time may come as well, so let us know what you find.

 

[JHZR2]

Ive cleaned the connectors that I am able to access. No help.

Im thinking it is just a flaky actuator - but which one? How to tell?

 

[TFB1]

Originally Posted By: Colt45ws
My thought it, even if one goes out the others should still work fine.


Agreed, should be a parallel circuit with each actuator oblivious to the operation of the others...

I doubt there is any adjustment, likely the actuators are worn out and need replacement...

 

[JHZR2]

So the guess is that the two side doors and the trunk all work intermittently but all fail at the same time? That's what is odd to me... Yet I hear the relay click without fail at the power lock brain.

 

[Kestas]

Make sure the actuator is getting power. The relay contacts may be burned, and need a cleaning or replacement. I find lots of problems right there with relays on electronic-laden vehicles that are in their second or third decade of use.

I too deal with old (10-20 year old) cars. As fdcg27 mentioned, there comes a time where the grease has hardened in the latch machanism. My fix is to remove the latch mechanism from the door, clean it in a parts washer, dry, then relube it with your favorite grease. If this doesn't appear to be the problem, then your actuator is getting arthritic.

 

[fdcg27]

Even worse, the car's central locking system also locks the fuel filler door, or at least it does on mine.
Not being able to add fuel could be a really bad scene.

 

[mechtech2]

Power locks and windows are problems waiting to happen.
I'd take it apart and lube all the parts.
If this is not THE problem, it is A problem that needs to be right to go on.

 

[fdcg27]

I dunno.
Both have been pretty reliable on the cars we've had.
OTOH, I've had to replace both of the driver's door PW assemblies on both of our Accords when each was twelve years old.
Had they failed in mid-winter or during the spring or fall storm season far from home, this would have been a problem.
I have never seen any real issue with cranking a window down, and I've never had a problem with a crank operated window regulator.
Also, manual locking and unlocking of the doors doesn't seem like any great hardship.

 

[TFB1]

Originally Posted By: fdcg27

Also, manual locking and unlocking of the doors doesn't seem like any great hardship.


I'd probably give up several other frivolous options before giving up my power locks... In a four door they can be real handy if you need to pickup passengers and doors are locked... Of course if said passengers left the windows rolled down, I'd be wanting the power windows back...

 

[JHZR2]

Manual ops is fine, I have other cars that require a key. But I've been spoiled by the keyless that I installed in this car.