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Polo 9N battery drain


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Pontoneer

Although I've been a member here for a few years , having had a few VAG cars myself , these days it is mainly for knowledge relevant to the various VW cars run by family members . 

 

My daughter has had her Polo 9N for almost three years - it is a 52 reg 1.4 petrol automatic car . While the car generally runs well , it has had one ongoing problem , that the battery often runs down to dead flat .

 

I used to largely blame this on the fact that my darling daughter hardly drives the car , tending to pinch her mum's new Mini whenever she can , rather than use her own petrol !! The upshot of this is the car can often sit for a month or longer between getting started , and then she might only go 5 or 10 miles in it ! There was only something like 340 miles between the last two MOTs . This is her first car and I've told her since she got it that she needs to use it more . However apart from this one issue the car hasn't given a moment's trouble .

 

Anyway , with recent events , I've spent the last few weeks around the house more than normal , so I decided to give the car a bit of an overhaul ; I was aware the exhaust system was on its last legs and fitted a complete new system ; also conscious that the battery repeatedly being allowed to go flat wasn't a good thing , I treated her to a new 63Ah Bosch S5 battery , thinking that , along with a bit more regular use , might solve the problems .

 

All was well for the first couple of weeks and she reported the car was going great . Pleased at this I felt it was money well spent . But then the other day , she told me she'd parked the car up on Wednesday , and on Friday it was dead flat again . She was going to get her step dad , who knows nothing about cars , to charge the battery , but I told her to leave it so that I could see for myself , and I went up the following morning ( last Saturday ) . As Gill had reported , even the remote central locking wasn't working and we had to open the car with the key ; there was no sign of lights having been left on , so I opened the bonnet and measured the battery voltage : zero ( and I have a decent Fluke auto ranging DMM which will register quite small voltages . Anyway , I had brought along another fully charged 100Ah battery out of my Mercedes 300SL , which i knew to be good , and jumped it off that , leaving the donor battery connected for a few minutes before attempting to start and also after it , to avoid too much of a drain on the alternator .

 

We drove the car the 10 miles or so to my house and parked it up while I ran Gill back home and then did some shopping . Some two of tree hours later , I went back out and checked the voltage ( it had been showing 12.7 V when we parked it ) and was down to 5.1 V ; admittedly it had only had a 20 minute run , so would not have been anywhere near fully charged . I put the battery on a maintenance charger and left it overnight , looking at the indicator on the battery charger yesterday , it was showing 12.8V and still charging , so I left it to today , when it was showing 13.3 V - more like it .

 

Anyway , I took the negative terminal off and put the meter in series , looking at current , when I reconnected through the meter , there was a loud clunk from somewhere below the windscreen , and the wipers jumped , and of course the alarm went off . However on cancelling the alarm , opening and shutting the door so the car wouldn't lock itself again , there was an initial reading of a little over 2A , before the car went into quiescent mode and the drain dropped to circa 0.15A which I didn't think too excessive . 

 

Pulling various fuses would reduce the current by 10mA here or there , but there were no huge consumers : once I figured that the fuse card referred to the box upside down , the two main draws were the dome light , which was off , fuse 28 ; and the cigar lighter , fuse 46 , I checked the lighter wasn't warm ( Gill is a non smoker so it is never used ) and left it out of the socket , just in case it was somehow drawing current . I checked for things like a light in the boot , and the glovebox , no problems there .

 

With the battery reconnected , showing 12.7 V before starting , and rising to 14.4 V with the engine running , I'm fairly confident the alternator is working and charging fine .

 

I did find this thread when looking for ideas , but couldn't see any other discussion re common problems .

 

 

The poster on that thread apparently had a door lock replaced by the dealership under warranty .

 

I'm now leaving the car overnight to see what happens . In the absence of any further ideas , all I can do it to try disconnecting various fuses until I see what might be the culprit ; oh , after reconnecting the battery , I discovered there is an auxiliary fusebox inside the lid on top of the battery , with about half a dozen fuses - I have no fuse map for these and no idea what they protect , but will try pulling each of them in turn tomorrow to see if the drain might be through one of them . 

 

I don't know if there are any known common faults on these cars which might cause the battery to drain . I now get the feeling this is something intermittent , either something like a door lock not fully latching , a wiper motor not fully parking , or water getting into something and causing a drain ( but haven't correlated these events to weather conditions yet ) , we did have heavy rain last week , so that is a possibility .

 

Any thoughts or ideas would be appreciated .

 

Thanks in anticipation .

 

Edited by Pontoneer
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Thank you very much . I will get my meter out this afternoon and see what current is flowing in each circuit .

Might pay to have a look at this https://www.clubpolo.co.uk/forums/topic/335902-testing-your-alternator/  just to rule out any problems with the alternator 

The odd-looking fuse in location 6 may be a 'ghetto' repair involving a thin sheet of metal, by the looks of it (or maybe a 175A fuse?).  That doesn't look like it'll do a particularly good job of pro

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Pete1

Does the battery symbol in the instrument cluster light up when you turn the ignition on (before extinguishing again once the engine is started)?

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Pontoneer

Yes , it does . The charging system appears to be fine . All lights are as they should be 

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Pete1

Ok, if you can post a photo of the battery-top fusebox, I could annotate it with the function of each fuse for you.

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Pontoneer

Thank you very much . I will get my meter out this afternoon and see what current is flowing in each circuit .

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Pontoneer
Posted (edited)

When I went out to check just now , the car started immediately , so the fault clearly is intermittent .

 

Re fuse 13 , that is just part of the plastic moulding below .The high current fuse on terminal 6 , I will see if there's anything written .

 

I will pull each of these fuses in turn with the car off and connect an ammeter across the terminals to see if any current in each circuit .

 

While I'm at it , if I can find it , I have an old Crypton automotive test set with a high current ammeter ( I think 50-0-50 A ) ; so I might take the alternator link out and see what current is being delivered ( don't want to blow the fuses in either my Fluke 122 or my old Avo 8 , each of which have max range of 10A )  ; I know the alternator is bringing the system voltage up to 14.4 V but if there is a fault in the rectifier pack , or worn brushes it could still be low on current delivery therefore not charging fully ( although that wouldn't explain the drain that happened over a couple of hours the other night , so I think I'm still chasing an intermittent fault . 

 

I will try starting and stopping the car , locking and unlocking it over the next few days and see how it goes .

 

Thanks again for all your help . It is appreciated .

Edited by Pontoneer
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Pete1

The odd-looking fuse in location 6 may be a 'ghetto' repair involving a thin sheet of metal, by the looks of it (or maybe a 175A fuse?).  That doesn't look like it'll do a particularly good job of protecting the wiring in the event of a short somewhere.  For reasons unknown, that particular one in that location is a common failure, by cracking rather than melting. I'm tempted to suspect vibration may be involved.

 

Halfords sell a 'variety pack' of different values of these style of strip fuses for a reasonable price, I seem to remember. 

 

For a really good indication of the true quiescent current, there's a dodge I described in the thread you linked in your first post. It involves a bit of dexterity, but basically inserts your current meter between battery post and clamp without ever breaking the circuit, so eliminating the chance of waking systems up that have fully gone to sleep state.

 

This is the process: 

 

Open the bonnet

Loosen but don't remove the battery negative clamp, make sure you can wiggle it free/off with minimal effort

Flick the bonnet latch over so that the car thinks the bonnet is shut, even though it isn't, giving you access to measure current directly at battery negative.

Lock the car, all doors. Making sure the key is outside the car.

Wait 30+ minutes. 

With multimeter on 200mA DC Current range (or similar) and probes in the appropriate meter sockets, put the negative/black meter probe onto the battery's negative post, straight downward. Hold the positive/red meter probe against the battery clamp in such a way that you can keep it on there (and the other one still on the battery post) while you gently jiggle the negative clamp up off the post around your black meter probe so that you now have everything connected through the meter (and the power to the car was never interrupted). This operation is probably much easier with an assistant, but quite doable solo.

 

Read the true quiescent current now.

 

Slip the negative battery clamp back down/on, remove meter probes, tighten clamp. Open up car and operate the bonnet release to reset the catch.

 

 

There's also a method of calculating the current through blade-type fuses by measuring mV drops across them in circuit, for similar reasons of non-interruption of circuits. First step is to find the true 'global' quiescent situation though.

 

Edited by Pete1
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Pontoneer
Posted (edited)
On 16/06/2020 at 13:47, Pete1 said:

The odd-looking fuse in location 6 may be a 'ghetto' repair involving a thin sheet of metal, by the looks of it (or maybe a 175A fuse?).  That doesn't look like it'll do a particularly good job of protecting the wiring in the event of a short somewhere.  For reasons unknown, that particular one in that location is a common failure, by cracking rather than melting. I'm tempted to suspect vibration may be involved.

 

Halfords sell a 'variety pack' of different values of these style of strip fuses for a reasonable price, I seem to remember. 

 

For a really good indication of the true quiescent current, there's a dodge I described in the thread you linked in your first post. It involves a bit of dexterity, but basically inserts your current meter between battery post and clamp without ever breaking the circuit, so eliminating the chance of waking systems up that have fully gone to sleep state.

 

This is the process: 

 

Open the bonnet

Loosen but don't remove the battery negative clamp, make sure you can wiggle it free/off with minimal effort

Flick the bonnet latch over so that the car thinks the bonnet is shut, even though it isn't, giving you access to measure current directly at battery negative.

Lock the car, all doors. Making sure the key is outside the car.

Wait 30+ minutes. 

With multimeter on 200mA DC Current range (or similar) and probes in the appropriate meter sockets, put the negative/black meter probe onto the battery's negative post, straight downward. Hold the positive/red meter probe against the battery clamp in such a way that you can keep it on there (and the other one still on the battery post) while you gently jiggle the negative clamp up off the post around your black meter probe so that you now have everything connected through the meter (and the power to the car was never interrupted). This operation is probably much easier with an assistant, but quite doable solo.

 

Read the true quiescent current now.

 

Slip the negative battery clamp back down/on, remove meter probes, tighten clamp. Open up car and operate the bonnet release to reset the catch.

 

 

There's also a method of calculating the current through blade-type fuses by measuring mV drops across them in circuit, for similar reasons of non-interruption of circuits. First step is to find the true 'global' quiescent situation though.

 

Hi ,

 

I have left the car over the last week or so , just trying to start it every couple of days , which it has never failed to do .

 

I wasn't aware of the switch on the bonnet catch , though , and pushed the latch over with a screwdriver . After doing that , the quiescent dropped from circa 115-120mA to 15-20mA , more acceptable in line with the document kindly supplied by Nigel . It was the same whether by your method above , or by disconnecting and then measuring . 

 

I had also disconnected the alternator cable and measured the current there - zero - so I guess I can discount the alternator .

 

That odd fuse in the position for the ABS pump has some writing on it - you can just see it in the photos above , looks like 150 , so maybe someone changed it ? I will go to Halfords and get a pack of these fuses and put in a 40A one . 

 

I'm now wondering if it might be the switch on the bonnet catch - since I don't expect it will cost much , I will see if the dealer parts dept has reopened and order one - I see the switch is inside a protective housing , but the bonnet catch has been liberally sprayed with some sort of grease , and nonetheless that switch is in quite an exposed position , so worth swapping it out .

 

This is one of those situations where I won't immediately know if the issue is fixed ; the car will need to go for a month or more without issue before I can be reasonably sure .

 

While at the dealer , I'll see if they'll give me the code for the radio , although I was going to get her a CD/Bluetooth unit rather than the old radio/cassette . However I will keep the original unit just in case the car is ever sold to someone who wants the original item . I did look through the pack of manuals and the card for the radio code had been torn out and is no longer present .

 

I have also bought Gill a solar charger , which I will wire up so it can sit on top of the dash ; hopefully this will provide enough charge to offset any drain , just in case I don't get to resolve this . 

 

I thank everyone for their help and comments , and I will pop back in to update ..... meanwhile it continues ....

Edited by Pontoneer
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Pete1

@Pontoneer If the tenth digit of the VIN is a 2, the microswitch is part number 6Q0953236C, if instead it's a 3, then the part numbers you want are 6Q0953236E and bracket 1C0 971 845, according to this page:

https://volkswagen.7zap.com/en/rdw/polo+derby+vento-ind/po/2002-253/8/823-823010/#17

The dates given in the data model column on that page are rather confusing, and suddenly (and only) make sense if you delete the leading '20' from each, which is some sort of glitch, I believe.

 

The suffix-E part number is slightly silly money new genuine e.g. https://www.allcarpartsfast.co.uk/vw-audi-seat-skoda/vw-audi-seat-skoda-6q0953236e-switch/.

 

There's one on ebay for rather less, but still a lot! https://www.ebay.co.uk/itm/6Q0953236E-VW-Polo-9N3-05-08-Bonnet-Lock-with-Micro-Switch-36-00-RRP/153774526178?epid=1917005592&hash=item23cdad0ee2:g:IZ0AAOSw9RZeA19h

 

The bracket may well be just to support the plug/skt connection so could be worked around economically with a cable tie or similar I imagine.

 

 

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Pontoneer

I should have come back before , but after fitting a new battery , the radio was asking for a code , which I never managed to obtain . In the meantime her battery had gone flat a couple of times .

 

Because her music was important to her , I gave her the almost new Sony unit I had bought for my own car ; in doing so , I found that someone had messed around with the wiring behind the radio , with the loom having been cut and joined with 'chocolate block' terminals . After some measurement with my multimeter , I reckoned I had identified all the wiring and connected the new radio up correctly - since then there has been no battery drain . It is only now , a few months later , that I can be reasonably certain the issue is sorted . Although I bought the new microswitch , I never fitted it , so I think it was incorrect/bodge up wiring by a previous owner that was the issue .

 

 

My daughter now appreciates having a modern radio which connects to her iPhone via Bluetooth and also plays CD's . Although she's 33 , such things are still important to her 🙂 

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Glad you got it sorted. Thanks for letting us know the real fault.

Seems like in cases of unexplained current drains, the default position should always be "It's the radio" until definitively proven not to be.

Edited by Pete1
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