Central Locking Pump Diagnostics

[sidrick]

I finally removed the CL pump from my car today (great guides from those that have BTDT ) after my car was refused an MOT test due to the boot not opening (doesn't open off key and CL stopped the day before test

Anyway, is there any way I can test that the fault is actually the pump? It's the early vacuum pump and when I turn he key to lock/unlock the door I can hear air being pushed in and out of the pump, but no motor or mechanical noise that you would normally associate with a working pump.

I've traced the driver side vacuum lines and they all seem fine, and since there's audible air entering and leaving the pump, I think the connections are all good. Is there anything I can check with my trusty multimeter before forking out for a new one?

[mdz]

Does pump runs ~2 seconds or more?

[sidrick]

Pump doesn't run at all.

[UrS4boy]

Pump doesn't run at all.

Did you check fuse No. 19 (or whatever it is on your S2)?

[sidrick]

Yeah, checked, double checked and replaced (wasn't blown)

[UrS4boy]

Yeah, checked, double checked and replaced (wasn't blown)

In that case, can you at least check that 12V is at the pump (shouldn't need the key on because it should be connected to the 30 bus, i.e. constant power).

[sidrick]

Initial in-the-dark testing would suggest I might not :\ I'll confirm tommorrow.

Where would be the next port of call if that was indeed the case?

[sidrick]

Can anyone confirm that there should be a constant 12v at the pump?

Edit: Car is a 1991 3B coupe, pump # 433 862 257H, which I believe differs from the later/ABY pumps.

[mdz]

Yes there must be constant 12v at the pump between red/blue and brown wires.

[sidrick]

There's definitely no constant live at the pump plug :\

Does anyone have a wiring schematic for the CL system?

[UrS4boy]

There's definitely no constant live at the pump plug :\
Does anyone have a wiring schematic for the CL system?

The power to the central locking pump has to be constant (not just with the ignition switched to ON) otherwise you would never be able to open the car with the remote (of course, this *is* your current problem).

There are lots of wiring diagrams at S2-audi.co.uk:

http://www.s2-audi.co.uk/workshop/schematics/schematics.htm

Specifically, I think you want to get into either the central locking schematics or the infra-red receiver schematics, or both. Good luck.

[sidrick]

The power to the central locking pump has to be constant (not just with the ignition switched to ON) otherwise you would never be able to open the car with the remote (of course, this *is* your current problem).

There are lots of wiring diagrams at S2-audi.co.uk:

http://www.s2-audi.co.uk/workshop/schematics/schematics.htm

Specifically, I think you want to get into either the central locking schematics or the infra-red receiver schematics, or both. Good luck.

Hi, thanks for the info

I don't have remote locking. This is purely from the key. I wasn't sure if a microswitch in the lock or something triggered the 12v to the pump, so I was just checking

[UrS4boy]

I don't have remote locking. This is purely from the key. I wasn't sure if a microswitch in the lock or something triggered the 12v to the pump, so I was just checking

Oh, in that case, while the power to the central locking system IS still going to be hot all the time , coming off the 30 bus bar via the S19 fuse. And, yes, the pump will be triggered by the microswitch in the door lock, as shown in this diagram from s2-audi.co.uk (F59 and F114):

[sidrick]

Thanks again, I've printed that out in A3 to help troubleshoot on Saturday.

There's power at the fuse, but none at the pump, so in my limited electrical experience I'd imagine I'm going to find something similar to what Newsh did - http://www.s2forum.com/forum/showthread.php?t=33420

[sidrick]

Gents, I'm still at this

So far -

1991, 3B, 'earlier' pump than the later cars.
Getting 12v to the pump for sure, fuse is also fine.
There is no air leak in the system.

First/original pump was brown bread, no life at all.

The next 3 pumps I have tried, 1) eBay special 2) known good 3) Brand new - all the same issue. Pump sounds like it's running, but it's actually a relay chattering inside the pump, not the motor. This will last for roughly one minute and the pump isn't pumping any air. Realistically should be able to rule out the pump itself now.....

What I'm starting to lean towards, and would like to know is, would a failed switch on one of the doors potentially cause this? Or does anyone else have any tips or advice before I start ripping even more of the car to bits to further trace wiring (which so far seems fine... despite being wet ).