A80 B4 central locking not working

[ert]

Hello, I have an issue with 1994 Audi 80 sedan central locking.

It doesn't work from either door lock or from IR remote. I have checked all door, hood and trunk switches, front door lock switches and trunk lock switch. The trunk lock switch doesn't work either way. I did those checks from locking pump connectors so the wires should also be fine (I also re-checked the trunk lock from the first connector right at the lock to rule out wiring issue).

I have tested the red-black and red-blue wires from 6 pin connector for power and brown wire for ground (used a H4 headlight bulb to load the wires properly).

When I grounded the white-yellow wire from trunk lock to imitate the lock being locked, a relay clicked inside the pump but nothing else happened.

When I open or close doors-trunk or pull-reconnect the brown 16 pin connector from the pump a relay starts to click inside the pump (randomly, sometimes it happens, sometimes it doesn't) like it usually does when it doesn't have a proper ground or power to it. The clicking lasts for maybe 30 seconds and then stops. I have tested two different pumps and they both act exactly the same way. Could it be the pump motor relay trying to turn the pump on and then turning off because no vacuum is being produced and locks don't move? The same as if there was a leak in the hoses? Then again why should the pump run when a door is being opened-closed?

When I apply vacuum or pressure to the hose at the pump all the locks lock and unlock properly.

What am I missing, doing wrong? Any ideas to what more to check? Or am I just having two broken pumps? I pulled out the board(s) from one of the pumps and there was visually nothing wrong, didn't do any other checks or soldering though.

[JayCab]

Hello ert,

It sounds to me like you've correctly diagnosed a broken pump, possibly the motor burnt out, possibly the internal solder (typically dry) joints on the PCB inside the pump module.

If you have actually taken the pump apart to PCB level, the next test would be to probe the actual motor posts and see if you get voltage and reverse voltage on the motor in response to lock/unlock actuation at the door / remote, to split between electrical fault or motor fault within the module.

Do you hear the motor at all, or just relays?
--> If you hear just relays, and the vacuum section is fine from pump pipe to all locks (sounds like you have diagnosed this), I would gamble the motor, relay contact, or PCB in the pump is at fault. I would take it apart and look for dry/separated joints on the power sections (trace back from the motor)

NOTE: I've not taken one of these apart personally, but I have re-soldered dry joints in the power window relays! I do know PCB solder joints are a very common issue. If you could

//misc waffle on time
I do know that when the lock/unlock is unsuccessful on these, the system response to to keep the power on the motor for a LONGER period of time (over 30 seconds) , waiting for actuation at the door locks that never happens (could call it vacuum timeout). This is why when you have a vacuum leak, you will hear the pump running continuously for a time but the doors will not lock/unlock, because the vacuum is not getting there and the locked/unlocked microswitch is not triggered, which would stop the pump ...


Hope this is of some help...

Hope you get it working again without (another) "new" motor....

[JayCab]

Note: When you say there is visually nothing wrong at PCB level, how closely have you looked? You can need a loupe to see dry/cracked/split solder joints, they are not always obvious to a glance. I've been caught out on this even knowing that....

It is of course possible the PCB is fine and the motor is burnt out, but I'd get VERY close to it with a magnifier before judging that, and I would only accept the motor is burnt out if I see voltage at the posts on actuation and no motion/vacuum.

[ert]

Thank you for your reply.

Hello ert,

It sounds to me like you've correctly diagnosed a broken pump, possibly the motor burnt out, possibly the internal solder (typically dry) joints on the PCB inside the pump module.

If you have actually taken the pump apart to PCB level, the next test would be to probe the actual motor posts and see if you get voltage and reverse voltage on the motor in response to lock/unlock actuation at the door / remote, to split between electrical fault or motor fault within the module.

Do you hear the motor at all, or just relays?
--> If you hear just relays, and the vacuum section is fine from pump pipe to all locks (sounds like you have diagnosed this), I would gamble the motor, relay contact, or PCB in the pump is at fault. I would take it apart and look for dry/separated joints on the power sections (trace back from the motor)

NOTE: I've not taken one of these apart personally, but I have re-soldered dry joints in the power window relays! I do know PCB solder joints are a very common issue. If you could

I took the pump apart right after testing powers and ground hoping for an easy fix. As I didn't find anything obvious I put it back together and started to test everything else on the wiring diagram. I will probably take it apart and just resolder everything and test the pump with external power source.

I haven't heard the motor(s) at all on either pump.

Note: When you say there is visually nothing wrong at PCB level, how closely have you looked? You can need a loupe to see dry/cracked/split solder joints, they are not always obvious to a glance. I've been caught out on this even knowing that....

I didn't investigate too much at that point. The pump actually has two boards on top of each other. As these pumps are easy to pull out from the casing I was hoping to see something obviously wrong but everything was visually fine.

[newsh]

I had issues with my central locking and courtesy lights in the coupe. It turned out to be breaks in the wiring loom under the carpet, the loom was bent sharply where it went into the trunking along the inner sill, moisture had got in and corroded the wires, I cut out the bad bits of wire and soldered in new, 10 years later still working fine!

For clarity, the breaks in the loom were at the bottom of the bulkhead where it meets the floor, below the drivers right foot (RHD car)

[ert]

As I did all the checks at the central locking pump connectors the wiring should be ok. Trunk wiring was broken near the hinge but I replaced a section of wires between the car and trunk before checking anything else.

At this point I'm presuming the issue is with the pump(s) but it would be nice if somebody came in and said that he had exactly the same issue and fixed it by doing this or that.

The only weird issue is that the trunk light stays on even if I close the latch while the trunk is open. The latch switch works fine.

[JayCab]

Hello ert,

It's suspicious that the boot light stays on when the boot is closed.

I would still do this next:
--> With doors and boot closed, probe the actual motor lugs on the PCB of the pump module while attempting lock/unlock.
--> You will find out if the system is attempting to lock/unlock, or not trying at all.
--> This will distinguish between wiring/control logic fault, and motor fault.

[ert]

Did some more thorough visual inspection of the board and found a blown capacitor. The diode next to it is fine. Will report back once the cap is replaced, will see whether it's the problem or just a problem.



The lower board is the power side and upper one is the logic board.

[JayCab]

Oooh well done! Before taking a soldering iron to anything...

I would still do this next:
--> With doors and boot closed, probe the actual motor lugs on the PCB of the pump module while attempting lock/unlock.
--> You will find out if the system is attempting to lock/unlock, or not trying at all.
--> This will distinguish between wiring/control logic fault, and motor fault.

If power and reverse power is present, board/logic is okay and motor is fried (replace whole module)

If no power at motor, then I would start soldering...
--> Replace blown cap you've found
--> Trace and reflow joints from motor back to power stage relay

I do look forward to hearing the outcome of this...I think you're onto a winner!

[ert]

It ended up being the pump motors fault (except for the blown cap obviously). I tested all diodes and transistors on the board, the ones that seemed shorted were fine after taking them off the board (you can only imagine the emotional rollercoaster I had).

I got both of the pumps-modules working after replacing the motors with Golf 3 or Passat 3/4 pump motors that I had laying around as spares for my A4 B5 in case it's propeller exploded at some point.

What I did notice messing around with these is that you have to be careful with tightening down the three screws that hold the graphite pump together (the three big yellow ones at the bottom of the pump) and on the metal backing that's screwed to the motor. If you tighten it down too much it will bind the propeller and require much more amps then what it should from the factory. I will test it out on some factory assembled pump to see how many amps does it take for the pump to turn on so that you can tighten the screws down the same amount after putting it back together (as the plastic outlets between the pump and motor are different on different models and need to be swapped over).

So a warning to anybody just unscrewing and screwing the pump up to check if the graphite propeller is fine.

I'm pretty sure the original pumps plastic casing was melted because of this (the pic). The bushing that is in the plastic was completely melted away. The windings were also dark.

Haven't got the IR remote to lock and unlock yet but at least the system works from door locks.

Should have listened to you JayCab earlier. Had i checked the pumps output sooner I wouldn't have had to check the components on the board. My thinking was that it can't be that easy. What usually dies first in electronics is the power supply-control circuits/components and I was pretty sure I was going to find a shorted transistor.

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