Remote central locking doesn't always lock

[5907]

The other day, I installed an aftermarket remote central locking kit in my W124, using a similar method to the one here:

http://www.mercedesshop.com//Wikka/W124Keyless

Although I didn't make any connections to the comfort module or relays, I just conected it to the vacuum pump.

The system seems to be working fine; the central locking still works normally with the key in both front doors and the tailgate, and unlocking works fine with the remote.

The trouble is, it won't always lock with the remote. If I try to lock the car with the remote right after I've unlocked it, it won't lock.

Usually if I leave it for a bit then come back and try to lock it again (using the remote) it will lock fine.

I'm fairly confident that the wiring is fine, because the unlock function always works fine, but locking is intermittent.

Thanks.

 

[television]

Check the time that the pump runs when locking, it should be no more than 3 to 4 seconds, if it runs longer then you have a vacuum leak

 

[5907]

Check the time that the pump runs when locking, it should be no more than 3 to 4 seconds, if it runs longer then you have a vacuum leak

Thanks television.

It does only run for a couple of seconds, and all the doors lock fine.

When I press the lock button, I can hear the RCL unit clicking (as it should) but no noise or action at all from the vacuum pump.

I think maybe the unit isn't always sending the right signal to lock the doors, though I've been through the manual that came with it and can't think why.

 

[television]

OK could this be a dirty switch contact on the door, if you can hear the RCL clicking then it is getting the signal.

Trying to work out if the signal is not quite right is not easy though if it is clicking it should be. Could there be a slight voltage drop on the power wires going to it, and it needs a recovery time before it can re set

 

[bigasotonuk]

I agree with your diagnosis Malc, You could check the power connections on the new RCL unit, and maybe worth checking your battery voltage too.

 

[5907]

I'll get my multimeter out and have a look.

 

[5907]

I had a look this morning, and the multimeter showed a power supply of just over 12v.

I then tried locking / unlocking with the engine running, and it locked & unlocked perfectly every time! My battery must be a little weak, although I've not had any trouble starting the car.

I'm quite relieved, I was worried that I would have to re-wire it all again. Thanks for the help.