I know this has probably been done to death but am having slightly different problems with the central locking on my early 89 928 S4 (non cat, european)
and it only started a few days ago

When locking from the key fob and central locking button it locks fine. when unlocking from the fob (or button) the pins only come up half way. If I press the central locking button a couple more times they gradually come up. Have disconnected each door actuator in turn but still the same. Have taken both door lock mechanisms apart, cleaned and greased them and they are free and work easily with the keys and ****. (They even occasionally work normally when the car has been running and left for a while, but only intermittently) So it appears to be a power issue.
Have been trying to find the central locking controller but cant find it anywhere!
(under center consol, under foot rest, under seats, under plug in cover, behind fuse board). Just cannot find it!
Could anyone shed light on the problem and/or suggest where the contoller might be? (assuming the 88/89 change over models actually have one and its not magic)

 

Sounds like someone installed an after market keyless entry. If not properly installed they can screw things up in a not fun to fix way.

 

If you are using a key fob button then I believe an after-market keyless entry system has been installed as I don't think that was ever available from the factory. That said, there is no telling where the central lock controller may be.

Mike

Edit: Woops, Sean beat me to the punch while I was distracted.

 

Hmm! Well the keys work it too but only occasionally opens both locks fully unless you turn the key to open twice. Yes its fitted with a laserline alarm and immobiliser. The box on the outer bulkhead (drivers side footwell) is unplugged and taped up. Im told that was the factory alarm? or could it be the ABS? argh! (Every workshop manual shows different)!

So you think they have bypassed the controller and removed it, and its working straight off the alarm/immobiliser system? I must admit that when an alarm agent changed a board in the alarm control box a while ago the opening sequence had a slight delay compared with before.

 

On my MY90 S4 LHD, the factory alarm relay is in that position (outer bulkhead RH footwell). IIRC the central lock controller is in the center console behind the ashtray. Best suggestion I have is to trace out the connections between the aftermarket alarm and the factory wiring harness and check/clean/renew all the connections.

Mike

 

Thanks will do that! The silver box up high in the footwell looks like an ECU with a huge multi-pin connector (Kinda like the ECU EZK on the other side)?

 

How's your battery and charging voltage? The same symptoms were part of a long list that were caused by some weak connections and low system voltage in my similar S4. Cleaning connections in the primary power wiring (at the battery, starter, alternator, and jump post) helped a little. Cleaning grounds helped a little, maybe, but they are all on the bi-annual electrical maintenance list anyway. In the end, tightening the alternator belt seemed to do the most good, by the way, and a replacement alternator is in the wings waiting for the right day to be installed.

Bottom line: With the solid primary connections and the proper charging, the locks are working correctly again.

 

Pulled out the alarm unit cleaned all the tabs, cleaned all connections from there to central locking button and doors. took out drivers locking mechanism and actuator, soaked everything in WD40, cleaned actuator, Cleaned and retightened battery leads, electrical sprayed the back of the fuse board, put em all back and seems to be working again. (for how long who knows) No idea which item caused it but thanks everone!