polecat702

On my 89 the central locking button stays lit all the time, but the doors don't lock or unlock. Is this unit seperate like on the 87's, or do I need to purchase the entire A/C unit also?

borland

Does the Speedometer Reset switch work? Could be the switch plate harness connector behind the switch plate is not fully seated.

Kevin R.

This is the exact same problem I have with MY 1990 928 but Roger was not available to reply to my thread from last night.

I thought it might be related to the alarm system malfunction as well but not likely.

It would be great just to have the central lock button work. Yes, it stays lit and only gives a "THUNK" sound when depressed. However, the exterior key cylinder portion of the central locking system works perfectly on both doors.

polecat702

I haven't tried the trip miles reset.

And mine makes the thunk sound but no movement with the door locks. My doors unlock seperately with the key. Are they supposed to unlock with the key in the drivers door, and unlock the passenger side when the drivers side is unlocked, and lock up the same way too?

MainePorsche

Locking/Unlocking with the Key should work on BOTH doors, as if you are pushing a functioning Central Locking/Unlocking Button.

Pull the center console carpet panels, unplug the harnesses (one on the Left - two on the Right) and remove the Central Locking/AC Switch panel. Inspect the solders and wiring on the rear. As you will see they can be problematic.

Add: Here's a pic of the back of the panel. Wouldn't take much to lose a connection

Kevin R.

Great idea!!!

I will go work on that one tonight and see what I find.

polecat702

Thanks all! I'll be working on this tonight also.

MainePorsche

I would start by evaluating the central locking panel. I now note your MY's and your harness(es) might be different, but no matter for the removal.

Kevin - sounds like you Central Lock/Unlock appropriately from the Key so hopefully a fix at the panel/button will solve.

polecat - yours doesn't function normally from the Key. I would eval the panel/button and get that out of the way. I'm knowledgeable on troubleshooting the 4 pin harness of the door lock motors. Your MY has a 5 pin harness at the motor. You may have a central and peripheral issue here. Someone will chime in on the 5 pin troubleshoot on your MY.

Kevin R.

Okay, all done... yes the MY 1990 is different then your photo and the harness is only 5 wires. Nonetheless, I removed and checked. All contact points solid. No trouble by visual examination.

I also noticed what that THUNK sound is. It is just the sound when the locks are being activated by the central locking button. As a test, I got in the car. Manually locked the doors by turning the dial on each door. Then hit the panel button and THUNK, the door locks opened.

SO, apparently the problem is the button fails to lock the doors.

What is the cause of the central locking button only working one way? Again, the button is bright lit all the time.

MainePorsche

Kevin,
Your MY has different wiring than my MY at the door lock motors and the lock cylinder (my MY has no wiring to the cylinder). I am comfortable with my wiring system, but not yours for troubleshooting/ testing at the harnesses.
After I trouble shot my problem at the harness(es) I concluded a wiring fault. My first thought was that it would be in the wiring bundle at the 'stress' point where the door hinges under the black tube. Sure enough I had a Brown ground wire severed there. Repaired the wire and my troubles were gone (I posted all this not to long ago).
Also, after I fixed the wire it worked. Then I tightened up the driver inside door handle recoil (it was a little loose and I would have to push it in). Well, I over tightened and and my doors would not lock from the button or either key. The motor would cycle and re-open. I couldn't lock the car! I finessed the tensioning and locking nut on the linkage and got the cosmetic/functional result I wanted at the handle along with my overall locking function. You may want to take a quick look at this - it is relatively easy and non major. Pull the panel above the armrest. There should be 2 push pins at the top to release then the panel lifts up from its clips easily. The handle linkage and adjustment are behind this. I am telling you this as possible causes, but again someone who is versed in your MY should chime in for the diagnostics.
Craig

borland

On my '90 S4, it works as described in the Owner's Manual, but for some reason, it gets confused if I cycle it too quickly. I have to cycle the ignition switch to get it working correctly again.

With the ignition in '0' position, it will also lock the doors (but not unlock them), button is not illuminated.

Kevin R.

As you know, my button is illuminated all the time (as if the system thinks the doors are LOCKED even when they are not.) The central locking button keeps UNLOCKING the already unlocked doors each time it is depressed. And yes, it does actually unlock locked doors but will never LOCK them.

Thank for the owners manual page. This is how it is to operate normally. That "cycle" ignition thing changes nothing for me.

Hey Borland, did you see the good report I left for you on that RDK thread?

borland

Kevin,

Since your seeing the button illuminated regardless of the ignition switch position (0, 0 & key removed, 1, or 2), you should investigate why the ignition switch is not powering down the illuminated button.

The central locking relay gets power from fuse 17, via Central Electronics panel plug K, pin 14 (RE/GN wire). Try temporarily removing fuse 17 to see if the controller resets like mine did. Then use your multimeter to see if power is removed at plug K, pin 14 (RE/GN wire) when the ignition switch is switched off.

Kevin R.

Borland,

Thanks for the detailed diagnostic procedure. I will get at this when I am at home with the car on Tuesday and report back, as I always do.

At least I have an angle to go with now.

Kevin R.

Okay, time to report today as promised...

When I removed Fuse 17, it made no difference other than I now had NO POWER at the central locking button with no illumination. It reset nothing.

With the voltmeter at K14, when fuse 17 was removed sure enough, the meter dropped to 0 indicating power was going though that terminal.

When the ignition switch was switched to the OFF position, the voltmeter reads that power is still present at plug K, pin 14 (RE/GN wire).

What does this indicate as it failed the final test?