Polo battery drain - Help!

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ripface
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Posts: 2
Joined: Sat Dec 19, 2020 2:46 pm
Drives: VW Polo 1.2 Mk4
Location: Grampian

Polo battery drain - Help!

Post by ripface »

Hi All,

My good ol' VW Polo 1.2 is causing me grief. The battery keeps dying needing a jump start every few days. Starting to run out of brownie points with friends and family due to frequent requests for rescues.

I've connected up a multimeter reading the amperage. At rest the battery is still pushing 0.74A which is way to high. Pulling the fuses reveals that Fuse 5 is the culprit as current draw drops to ~0.02A when that fuse is pulled. It seems that this is the engine management fuse, but how to troubleshoot further is more of a mystery.

Is there a common issue with the engine management that can result in a component drawing excess current when the car is switched off? Hoping someone has seen a similar issue and knows the best goto component that might be the culprit.

Thanks,
Ripface.
RUM4MO
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Drives: B8 S4 & 6R/6C1 1.2TSI 110
Location: Mid Lothian

Re: Polo battery drain - Help!

Post by RUM4MO »

You really do need to check the drain after all the systems have been forced into a low activity, ie sleep mode.

How I do this is, using a multi meter, connect one side of the ammeter to the earth point near the battery, using a second lead which has a long thin probe, press this down onto the battery earth side post, while holding this down, loosen off the battery -VE lead and ease it up over the probe, so the current meter will now only read the "sleep" drain current.

That might reveal either a high constant drain current, or a low "within spec" drain current - but either of them might only be a picture of what is going on during that instant, outside that time window, who knows and that can be an issue.

Don't fall into the trap that the fuse that you have pulled is the only or correct fuse, these smart controllers will use a single fuse to power their control side, other fuses will be on their switched loads sides - so the fuse that you have pulled probably powers a controller, ie a power supply switching unit while it might be actually one of that unit's outputs or loads that is the problem, keep an open mind when trying to solve this, it might take quite a long time to find the root cause.

I've been there done that with a late 2009 SEAT Ibiza 1.4 16V SC - I worked out it was a software issue with its BCM which controls the powered loads, but it took 2 SEAT dealerships to accept that and request a fix from SEAT Mothership, VW also had the same issue on some same age Polos, though I don't think that in your case this is your issue - unless you have heard similar stories covering your age of Polo.
ripface
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Posts: 2
Joined: Sat Dec 19, 2020 2:46 pm
Drives: VW Polo 1.2 Mk4
Location: Grampian

Re: Polo battery drain - Help!

Post by ripface »

Hi RUM4MO,

Thanks for taking the time to reply to my query. When I was testing the current draw, the keys were out and the interior light disabled. I waited 10 mins to make sure the car was definitely "sleeping". The Multimeter was using proper clamp probes between the battery terminal and the terminal clamp. Initially I was confused as the meter was reading 0.02A which I considered normal, but when I returned after ten minutes the draw had jumped to the 0.74A. Pulling fuse 5 consistently returned the draw to a nominal value and replacing it jumped back up to the 0.74A.

I'll do the test again bearing in mind your comments. Thanks again for the pointers.

Regards,
Ripface
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