Central Locking Issue (not a leak or a dead pump)

[christenkonrad]

Hello everyone,

I'm looking for support in resolving an issue I'm having with my central locking on my 1994 S6 Avant.

What's happening now is that I press the lock button on the drivers side door, or turn the key in the drivers door to the lock position and the pump doesn't engage. I can hear a relay click or something back by the pump (I think) but no pump whirring to life. Has anyone experienced this problem before? Can you give me an idea of if there's anything I can try short of just replacing the pump again?

To clarify, if I lock the doors manually, and push the unlock button (or turn the key to the unlock position) the pump will whirr to live and unlock the doors without incident. It's only the "lock" function that isn't functional. I also confirmed that holding the key in the lock position will raise all the windows.

Background on how I got here:
-I had a non functional central locking system.
-I replaced the pump and got suction and found I had a leak.
-I fixed the leak (hatch locking actuator boot)
-I had functional central locking
-I replaced the vehicle battery
-now I have a non functional lock button.

I would appreciate any recommendations that anyone has or any personal experience with the same situation. I have tried to use the search tool and I keep getting posts about leaks or dead pumps so I apologize if I missed a thread on this.

Thank you very much!

[Nuvo]

First things first, you should be commended for setting out the problem so clearly and describing everything that you have done up to this point.
My thinking is that the remote control may have lost sync since replacing the car battery and it will need to be reprogrammed.

I seem to recall there was a guide on how to do this posted on here before, it might be for a first generation A8 but it can be used on other cars of this era as it shares the same controller. I'll post a link here if I can find it for you.

Here's one link so far. https://www.s2forum.com/forum/techni...is#post2157615

[Nuvo]

This may also be of help: https://www.s2forum.com/forum/techni...ng#post2156325

[HPsauce]

Just to do a bit more diagnosis, do you have a radio remote for this car or are you only using physical keys (and door button) to lock/unlock?
If you have a radio remote I would advise resyncing it to the car (IIRC a relatively simple process for that generation, Google should find it) then seeing what happens re locking/unlocking/boot and report back.
If you get the same partial "central" function (unlock but not locking) it points to either controller or pump, not sure how separate those are for that vehicle.

[JayCab]

“lock” function not working via key or internal button
—> so unlikely to be input related

unlock activating pump pressure, but lock not activating vacuum
—> unlikely to be pump itself (but possible, on the control board)

It could be normal behaviour for lock to be disabled if the car thinks the doors are open
—> Does the interior light go on/off in response to door close when set to door position for all doors? If not, check door contacts
—> Same for tailgate

If all the above checks out, I would probe the harness connecting to the pump for the lock live signal coming from door button and key switch, to distinguish between vehicle electrics and the pump electrics, then troubleshoot either side…vehicle harness or pump PCB…

[christenkonrad]

Thank you all for your prompt responses!

I didn’t realize it was possible to have a key fob to lock/unlock so I apologize for not being more clear. I only have the button on the drivers side door so that’s what I was referencing.

I reviewed the troubleshooting the other gentleman went through and the recommendations above and I think my new hope is a bad solder joint.

I will disassemble and check what I can. It’s my impression that since I can hear a relay click noise, I think signal is making it to the pump electronics and it’s trying to engage the pump but power doesn’t flow, but only in the one direction.

thanks again for the advice and input!

[JayCab]

Great!

…in which case, I’d head straight for the power contacts driving the motor as the next point of call, tracing back to the relay..

…this is super-common with electric window relays. The current carrying contacts go dry first…

let us know how it goes and what the solution ends up being

[christenkonrad]

Good news, bad news.


Reflowing fixed my issue, the lock button and key turning now correctly engage the pump.

However now the pump is running and it feels like it’s doing something at the output hole but the doors neither unlock nor lock….. I don’t hear any leaks anywhere inside the car and it’s unlikely I created any leaks in the car system simply by removing the assembly from the car. Except the rubber connector around the nub of the assembly but the rubber nub is intact.

I did not have to remove the pump itself from the assembly and only pulled out the circuit boards and reflowed everything on the power path from the center connector to the switching relay to the motor wires.

I’m an EE who has experience working on small electronics so I think it’s unlikely that I crossed some pads but I’m not sure what could have caused it to be weaker.

Does pulling out the circuit boards potentially unseat the pump connections to the output?

[christenkonrad]

Follow up.

I confirmed it is blowing outwards when locking and I can’t tell if it’s really sucking inwards when unlocking.

I can feel output from the main output hose when locking, but for unlocking it just feels like the thing is vibrating and maybe has the slightest suction but nothing conclusive.

[christenkonrad]

The pump function appears intermittent but now it’s always failing to actuate any unlock or lock function.

After unplugging, messing with, and replugging sometimes the lock button does nothing and sometimes it does something.

this may be indicative of a wiring issue that’s being jiggled when I’m unplugging and replugging.

But now I’ve taken a system that was previously able to lock and unlock and created a system where the pump runs but I can’t unlock or lock anything.

No leaks can be heard.

I was able to blow into the line to get the gas door to unlock after noticing that was stuck locked.

[JayCab]

I wouldn’t gamble that not hearing any leaks means there are no leaks. it would only need to be small, most of the lines are behind panels and carpet, and the actuators are inside the doors behind sound insulation..

The actuator diaphragms can bleed slowly. a leak on any one would throw the whole system.

Can you test with a large volume syringe at the pump input pipe. Does the system actually lock/unlock when vacuum / pressure are applied to the system?

If the motor spins in both directions for lock/unlock, and you think the switch is dodgy/already explained, then there really must be a mechanical/vacuum problem…

You could be really unlucky and have a partial vac leak and a half burnt out pump, with the former causing the later…

[JayCab]

If you find a blown actuator, don't bother trying to repair it. Total waste of time. Replace them. Ask me how I know

[ert]

I did not have to remove the pump itself from the assembly and only pulled out the circuit boards and reflowed everything on the power path from the center connector to the switching relay to the motor wires.

Does pulling out the circuit boards potentially unseat the pump connections to the output?

Yes, there are rubber connection(s) inside that need to be put back. They connect the pump to the board and the part that you connect the line outside of the pump.

Can you test with a large volume syringe at the pump input pipe. Does the system actually lock/unlock when vacuum / pressure are applied to the system?

Do that, this way you can understand if the issue is on the car side or the pump side (but use a syringe or a hand pump or something other than a compressor, the system uses low psi).

After unplugging, messing with, and replugging sometimes the lock button does nothing and sometimes it does something.

this may be indicative of a wiring issue that’s being jiggled when I’m unplugging and replugging.

Could very well be. Find a wiring diagram (quick google search will help you with that) and you can check all the components at the pump connections, it's actually pretty simple system.
Be aware that the electric motor can overheat when you make it run a lot.

[christenkonrad]

Thank you gentlemen for the input!

I am thinking it's possible I could've unseated one of those rubber connections because it's just too weird for everything working going to suddenly nothing working.

I will test using a syringe or hand pump if I can to confirm if the system is operational or not. I'm guessing I couldn't exert enough pressure on my own to actuate anything except the fuel door lock.

I did find a diagram and used it to ensure I reflowed the proper junctions on the board. I will take another look. Quite frankly I was so frustrated after I found it didn't work anymore that I just reinstalled everything and parked her. I feel like I've been fighting the good fight trying to bring this ole girl back to life and she's just fighting back in the silliest of ways.

Thanks again for the advice and things to try!