A friend came to me with his 2006 Fabia 1.2l asking me if I could help him solve his electrical related problem. He said that his battery drains by itself overnight. I asked him if he has recently installed any non-factory electrical device. He told me he purchased and installed a cheap anti-theft + remote central locking device.

 

Long story short, I measured a 5.2 A stand-by current... which raised to 16.5 A with ignition key on...

I started to disconnect the fuses one by one and here is what I have found:

 

ALL CONSUMERS OFF, IGNITION KEY OFF

- the circuit with fuse 4 (interior light, glove box light, luggage compartment light) draws 0.5 A

- the circuit with fuse 43 (onboard supply control unit) draws 4.3 A

- the circuit with fuse 45 (radio) draws 0.1 A

- the circuit with fuse 49 (central locking) draws 0.3 A

 

I removed the fuse of the alarm/remote CL but nothing changed. Even stranger, turning on the interior light raised the current consumption from 5.2 A to 8.6 A!! 3.4 A for a 10W bulb?? But wait, that's not all. Turning on the side lights (25W in total) raised the current consumption from 5.2 A to 21.6 A !!!

 

What is going on? I think it is something related with onboard supply control unit but I don't know exactly how that 'computer' works. Can you help, please?

Edited 14 February, 201511 yr by RicardoM

Have you tried to measure the amps drained from the battery with the car locked ? 

Yes, that was the first thing to do. Replicate the symptoms. The same thing happens. Same currents. As I said, the battery drains overnight and ithe car is left locked obviously.

I'd suspect the anti--theft device (and why bother anyway? Presuming your spec to be the same as European here, the car already has a transponder immobiliser fitted). Have you tried disconnecting it yet?

 

Beyond that, I'm afraid I'm left agreeing about the OSCU, and suspecting that it was damaged by the anti-theft (either during installation with battery connected, or by a design unsuited to the car).

With the unexpectedness of some of those measurements (sidelights etc.) I'd be thinking that there's something wrong with your meter. Is there another one you could use to cross-check?

My meter is good, cross-checked it with an Agilent I borrowed. In fact, when I turned on the side lights, the probe wires got warm.

 

I agree there is something fishy about that alarm design or about the connections made to the original wiring of the car. About using the alarm, the car is not mine, I said that, the guy wants it on.

 

I could easily disconnect it, but I am more interested in WHY the alarm messes so badly the Electrical system control unit or the Convenience system central control unit. The latter I suspect is the most affected by the intruding alarm. I say that because the central locking doesn't work anymore using the key of the car (it locks then unlocks immediately) but it works from the remote of alarm.

 

So I would like to ask you guys 2 things:

1. where can I read in \depth about how the Convenience system central control unit works? The best resource I've found so far is SSP 33 from VAG Group, but it is too generic.
2. have you heard of any situation when the Electrical system control unit failed? Why?

SSP265 part1 comes closest to being helpful to you, I think, but even the promising looking block diagram of J519 on pages 22/23 lacks the necessary detail to really be helpful.

It just shows everything that connects to that module, not what's inside.

I haven't heard of a case, but I imagine water getting onto/into any of the electronics modules might be one mechanism for unexpectedly-large current flows.

Ricardo, my concern is that the alarm is the cause of the problems, and they can't be fixed any way other than by removing that alarm. I wasn't asking to remove it permanently as first action; just to disconnect it and see if that cures the problem to prove that the alarm is the cause. OK?

 

The point about the transponder immobiliser was that, even without the alarm, you can not steal the car without a low loader or the ignition key. Does your friend realise this?

 

If he does, and still insists on an aftermarket alarm, then if we can prove that one faulty, we can make progress.

Thank you guys. I have started reading VW SSP 265 and it is much better than Skoda SSP 33. Polo 2002 is very similar.

I will disconnect the alarm temporarily. Is there a good generic guide on how to install properly a third party alarm system on a Fabia I fitted from factory with central locking from door locks (no remote) ?

I very much doubt it because, for obvious reasons, not all alarms are the same beyond that they need to be connected to a permanent live feed.

 

This may be more than he'll want to pay, but there are VAG perimeter + volumetric alarms.

Update: I took out the alarm and restored the original wiring. The central locking works now using the key of the car. The stand-by current consumption dropped from 5.2 A to 1.9 A. Still too much. I waited 35 minutes to see if the Electrical system control unit kicks in and lowers the current to less than 25 mA. No luck.

 

I didn't have a VCDS scanner so we took the car to a local dealer. The verdict came fast. The alarm had not been installed properly from the beginning. It eventually failed and in turn the Electrical system control unit became faulty. Ouch.

 

Ok then, let's forget the generic alarm system install guide. The remaining questions after this happening are very straightforward.

• Where should be connected the Lock and Unlock outputs of any alarm ?
• What type of Lock and Unlock signals expect Fabia's computers ?

A schematic would do wonders.

Edited 18 February, 201511 yr by RicardoM

Ok thanks Ricardo. I'm afraid that my worst fears have been realised this time.

 

I can give some general advice about installing alarms (but it's too late for your friend :( ):-

1. Disconnect the battery.
2. Disconnect the battery. Ok, I know I said that twice but it is that important.
3. Cut and solder all connections. Make waterproof with shrink-wrap. DO NOT use bodge-loks.

Thanks, but everything you said is the ABC of installing an alarm, I asked more specific questions about central locking.

1. where in FABIA I wiring should be connected the LOCK/UNLOCK outputs of an alarm?
2. any diodes, resistors or relays needed?
3. what polarity/duration should have the LOCK/UNLOCK signals?

Edited 19 February, 201511 yr by RicardoM