Help, my daughter’s polo battery keeps going flat. Changed it for a new one but same problem.  With everything switched off it’s drAwing just over an amp and when fuse F30 is removed it drops to about 330mA.  I believe F30 is for the multifunction control module (whatever that is?) all help appreciated as now stumped…

The control unit in question lives above the accelerator pedal and has lots of multiway connectors hanging down out of it.

It may have suffered an internal component failure which I've seen a few times, where a surface mount ceramic capacitor ends up looking very 'nuked'.

The simplest fix is to replace the unit with another with exactly the same part number from a car as near identical as you can find (and hope that it doesn't have such troubles).  The part number of the unit is on the side facing downwards when installed, so should be visible without more than a little contortionism (an outstretched phone camera may avoid any such pain).

 

New replacement will be big bucks, so not advisable really.   

There is a modicum of configurability to these units, and a simple/1 minute process with VCDS to read the config code out of the old one, and put it into the replacement unit (or read that one's current config and possibly find it's already the same).

 

Unplugging the many connectors can be a bit awkward, they can be quite 'sticky' if never previously undone.

 

If you wish to eyeball the circuitboard inside, the unit comes out of the car quite easily once the connectors are all out, and then the case splits with just four simple clips on the sides.

 

 

 

 

 

 

This is one that has really 'gone up well'. If you see something like that I'd say you have found the problem.

 

 

Remember this well Pete,Remember contacting several breakers all of them who had the same unit had the same fault,only plus was as soon as repaired unit fitted,no more flat batteries 

This was the thread where you brought up the issue with yours (posts starting Sept 2020) : 

Depending on the part number that Clive finds, I may have a unit kicking around that would do the job.

You certainly saved the day,I hope Clive is as lucky,it was a shame we were unable to meet up to do the exchange,bad year 2020 

Fingers crossed, I may have found the problem.  We’ve had the car 10 years and had a black box fitted by the insurance company when we first got it. I found some add on wiring by the fuses which I think are black box related. I’ve unplugged it and drain has dropped to about 250mA.  Not sure if this is low enough but looking much better. I think it was linked to the wiring associated with F30. I’ll see if the battery holds its charge over a few days and report back. Meanwhile I better contact the insurance company and check it’s not used anymore.  Many thanks for all the help. 

250mA is still very high,  it should be around a tenth of that or less, but needs measuring in a specific way to ensure everything is properly 'asleep' when the measurement is done.

 

Removing that box sounds like a good step in the right direction though.

Help very much appreciated. Any thoughts on where the 250mA might be coming from? I’ve had all the fuses out but it’s still there. I give the ammeter plenty of time to settle down as it’s higher to start with.  Many thanks

Forgot to mention my airbag light is now on. 

10 minutes ago, Clive Chapman said:

Any thoughts on where the 250mA might be coming from?

Possible alternator diode fault?

In the fusebox above the battery there are a row of strip fuses, the first (nearest engine) of which is the output connection from the alternator.  Try disconnecting the wire from the front end of that fuse and see if the drain disappears.

If it doesn't, you could try the same on each of the other strip fuses in turn. 

There are also a few blade fuses under an adjacent cover that could be checked, follow the smaller wires to find them.

 

 

 

 

 

Edited 29 April, 20224 yr by Pete1

As pete said earlier I would check the module under the dash,Clive you sound very much like me,I even went down the black box route,changed alternator etc 

Removing the wire from the second of the strip fuses would check/eliminate everything in the cabin as it is the feed to the internal fusebox.

Now I think about it, I think by finding that the 250mA drain is still there with F30 out, you've probably ruled out that control unit as the problem.

Edited 29 April, 20224 yr by Pete1

Have a read of this https://www.clubpolo.co.uk/topic/335902-testing-your-alternator/ just to eliminate leaky diodes in the alternator 

 

Good news, things are getting better, when I take out the fuse in the photo I’m down to 150mA…

if I disconnect the second lead as well I’m down to practically zero but only if I also take out the fuse otherwise I’m around 200mA

 

Any ideas what this fuse is for? 
 

Many thanks 

 

What year is the car,  please? And did that come out of the slot number 11, or 9? 

 

Ah, it must've been in slot 11, no contacts visible in slot 9.

Radiator fan control unit, at first glance; situated near bottom hose of radiator, hanging off a bracket on inside of chassis leg.

Observation about second lead (cabin feed?) wire/fuse is odd. 

Edit: Ah, maybe I just misinterpreted what you meant by 'the fuse'. Presumably you meant the fuse in slot 11, not the strip fuse that the cabin feed wire connects to?

Edited 29 April, 20224 yr by Pete1

The fuse is from slot 11, the Polo is an 03 1.2E. 
 

sorry for the confusion, I meant the strip fuse where you have to disconnect the wire with a nut.

 

so if it’s radiator fan I guess not a good idea to just disconnect it and hope for the best

Forgot to mention it’s a 5 amp fuse

Don't jump to the conclusion that the fan control module is faulty by the way, it sounds a bit like the relay coil which that fuse feeds in the FCM is being energised by something in the cabin (spuriously), and isn't when the main cabin feed is removed, I think.

 

I can't get my head around

5 minutes ago, Clive Chapman said:

sorry for the confusion, I meant the strip fuse where you have to disconnect the wire with a nut.

 

Do you mean that you have to remove the nut/wire and that strip fuse (rather than fuse 11) before the current drops to near zero?

That’s right, I have to remove the nut and wire plus the 5 amp removable fuse to get the leakage to virtually nothing but if I just remove the nut and wire I still get approx 200mA leakage.  If I leave the nut and wire on and remove the 5 amp fuse I get down to a bit less than 150mA

The circuitry on the end of that fuse is the top bit of this sketch labelled 86a, which is what's inside the FCM.  

I suspect that the input (pin 5 of the 6-way) that gets pulled down by the A/C control module in the cabin is being wrongly pulled down for some reason, resulting in that relay coil being on all the time.  That ought to bring the radiator fan on at low speed, but there's a common failure that might be separately preventing that.  Is the 30A green fuse in position 8 in your pic intact?  That's the feed that supplies the fan motors at low speed, top right in the sketch:

 

Edited 29 April, 20224 yr by Pete1

Many thanks Pete,

Just checked the green fuse, it’s fine.  Where will I find the FCM, is it one of the relays by the main fuse box?
 

 

2 hours ago, Pete1 said:

situated near bottom hose of radiator, hanging off a bracket on inside of chassis leg.

 Rectangular box with white writing on, slap bang in the middle of this photo

Edited 29 April, 20224 yr by Pete1

Does this car have two rad fans, a little one and a larger one?