Weird car problem – any ideas ?

I’ve been having a weird serie of electrical problems with my VW Polo that don’t make logical sense to me – maybe because I have no clue how these things work. Maybe someone has some ideas on what might be happening?  Basically the EPC light comes on. I gather that this is a catch-all system that is triggered by any number of problems and generates codes that can be read by a magic box. The car drives fine but then develops a series of problems:

auto stop/start system doesn’t work (the thing that turns off the engine when you stop at traffic lights etc)

parking sensors don’t work

a/c doesn’t work

electric mirror adjustment thingy doesn’t work

maybe other stuff I haven’t noticed yet.

I’ve just come back from the dealer who said they’d read the diagnostics and replaced a fuse and all was fine. I drove off happily and 2 minutes up the road the EPC light is back on and there is a message saying the auto stop/start system is not working. The other stuff in my list still works.

What I don’t understand is, well, many things – first of all, if these problems are down to a fuse, why is it not “all or nothing”? Why is just one of my list of problems happening now and not all of them? I’ll have to take the car back, but it’s a real hassle so I’ll probably leave it a bit to see if more problems develop.

Any information or ideas about what could be the issue (I doubt it’s just the fuse, clearly) or just sympathetic noises, would be appreciated !!

If the start/stop doesn’t work can you get the battery checked?
No idea about the other stuff but maybe start with the basics!!

Not a VW but pretty much everyone experiencing electrical weirdness in my car model eventually trace it back to a duff battery. Would be the first thing I checked.

It’ll be a control module somewhere that’s either got wet or dry solder joints or something.

Had similar with my Beemer. Start it up – full festive christmas dashboard, headlights flickering, non functioning indicators (no one else noticed), no e/windows, no e/mirrors random bings and bongs. TIOABOA and it might be fine again, it might not. Figured out after a bit it was a footwell module and if it acted up you could unplug it, replug it and it would be fine until the next time you started the car, where you tossed the coin again. Secondhand one off ebay and a coding sorted it.

Fuse swap will have been the equivalent of unplugging the module and giving it a hard reset. Find out what fuse it was and what module(s) it supplies to narrow it down.

If the car doesn’t go for long runs the Stop/Start function can become temperamental…a couple of decent runs tends to sort it out for a bit. I think the battery just needs a good recharge.

My secret fear – that I can hardly bear to write down – is that the mice who chewed the fuel line last year leading to weeks of work and massive expense have returned with a taste for electrical wires. Or at least the casing. :-( :-( :-(

How old is the car? Could well be the mice. But VAG cars really don’t like poorly batteries. So my first thought would be to check the voltage the battery is pumping out.

+1 for battery, I had a car once that threw all sorts of oddities when the battery started to die including switching it’s 4×4 system off whenever the brakes were pressed (halogen brake lights are a massive amp draw).

How old is the car?

It’s a 2015

Could well be the mice

Stop it stop it stopit !!!

EPC = Electronic Power Control

So the power distribution node, distributing power to all the other nodes. Which don’t work properly.

90% chance that yer battery is on the way out, or you’re doing too many short journeys and not charging it properly.

Other 10% is that whatever circuit board the EPC is attached to/installed in has a dodgy connector/track/joint.

Battery conditioning charger will be 20-30 quid, battery will be ~100 quid, controller will likely be several hundred.

Take your pick.

(Check if your car is one that has 2 batteries or not, i know there are a few out there, one big “car” battery and a smaller gel-pack battery stashed away somewhere to keep the lights on when the engine isn’t running. You could get these symptoms if either of them fail, or fail to charge properly.)

Battery.

golfs from that year (mine) have an easy way to check the battery. Dunno if it works on a polo but here goes:

Battery first for that age.

So would it be worth just having the battery replaced at a local garage right away, bearing in mind that the dealer charges over a hundred quid an hour just to look at the problem?

get a code reader yourself (£20 or so for a basic one on amazon) and find out what the car actually thinks is wrong. It could well be a fuse that’s repeatedly blowing due to a short somewhere else.

If the start/stop doesn’t work can you get the battery checked?

Stop/start on my 2021 Ducato seems to have a mind of its own. No rhyme not reason as to when it decides it’ll kick in.

Stop/start system working seems dependant on a number of reasons. 

So would it be worth just having the battery replaced at a local garage right away

I’m leaning towards yes, since your symptoms point strongly towards this IME.

However, how old is the battery? 5 years or more almost certainly needs doing regardless of whether it’s the root cause.

No need to go to a main dealer. I’d actually recommend your local Halfords shop (not autocentre) if it’s convenient to you. Decent online booking system and they’ll drop the battery in in the car park.

Yes to the battery, I picked up a quality one from my local motor factor for under a ton for my polo. Very simple to fit although I appreciate you may not have the time to do it. The Halfords option isn’t a bad call.

Previous vws of mine have been a bit funny with damp, control units getting wet and throwing various levels of weirdness

I’ve just come back from the dealer who said they’d read the diagnostics

It’s a shit garage if they didn’t give you a print-out, and at least test the battery.

Worth noting that some cars need coding when you fit a fresh battery, which is a pain for such a simple job.

Wiring harness issue, dodgy earth maybe. Try battery or get it load tested

Having had similar a few weeks back in a Ford. 

Battery seems the best case/ low cost cause.  

A decent garage should be able to test the battery without you buying a new one on the off chance. If you have start stop there may be a more expensive battery option you need.  Turns out mine had had an internal failure of some of the cells.  New battery job done.  

We had a 2015 Polo. Advice to change the battery is solid IMO. However, we also had problems caused by the gubbins that connects the buttons on the steering wheel with the rest of the electronics. It made a clicking noise when steering was on full lock…

If it does need a new battery make sure you get the right one, check it’s the exact right one – because a not-quite right one is a PITA.

Yes, start-stop cars need a different type of battery called AGM but they are clearly labelled as start stop compatible.

@Drj Yeah, to get into a repairers you’ll need to call them at 08:00 to get on the list. At 08:01, the list will be full. You’ll spend hours trying to get through then when you do, you’ll be able to book a call back with the tea girl/boy in February 2024.

Bon courage… 🤣

Did the dealer do any fault finding beyond read the codes? I would, perhaps naively, expect them to have tested the battery? Depends what you asked them to do I guess 🤷‍♂️