Hi there I have the above problem, sometimes even after a long drive!

 

Had a battery diagnostics done and battery is in good condition (it is an expensive stop/start battery).

 

I’ve been driving around for last week with a voltage display plugged into the cigarette lighter:

 

about half the time it reads 14.8v

the other half of the time it reads 13.2v

 

when it reads 13.2v the car automatically disables start/stop. 
Also I’ve noticed the car idles quite rough when at this lower voltage.

 

one other symptom (might not be related) is a very loud fuel pump noise when starting the car.

 

 

thanks, any ideas would be much appreciated 👍

 

 

Welcome.

 

Sorry no idea. Maybe tell others what engine your car has.  Not that it makes much difference but good to know.

1 hour ago, Rooted said:

Welcome.

 

Sorry no idea. Maybe tell others what engine your car has.  Not that it makes much difference but good to know.

oh yeah, thanks.

 

2.0 TDI estate

Hello, welcome to the forum. If your battery tests as OK - and your alternator voltages look good, I'd suggest that there is something not 'going to sleep' correctly after you shut down.

Check the forum for parasitic drain on battery. The noisy fuel pump should not be the cause (unless it keeps running after engine shut down)

Were there any changes made to the vehicle around the time this problem started?  

Ye agree with above. 

Go out in the dark and see if you can see anything lit up. 

Not just outside but inside car. 

After a long run, can you start the car or is the battery flat?

 

 

Just saying ‘the battery tests okay’ is not massively helpful as many will now skip over the battery without wondering it if it truly okay.

 

what kind of test was done? When was the test done? What equipment was used? What were the specific results of the test?

 

An example could be the battery tests okay - with a multimeter - at 13.8V - 5 seconds after the car has been switched off.

it doesn’t test the battery properly nor paint a complete picture of the batteries health so is a false diagnosis.

 

If a good test has been done and the battery is still dying then a current drain test is next using a non invasive method - if you do the old school method of pulling fuses and putting an ammeter in place the vehicle will be constantly woken/activated by different canbus modules. An inductive current clamp or thermal imager is the only correct way  to accurately monitor any current draws 

 

but before that the battery, charging and driving style need to be confirmed as good.

I doubt what I suggest is the cause but MkI Fabia's had a common fault where the alternator load sensor wire failed resulting in not keeping the battery charged sufficiently. It's worth considering as from memory it was a relatively simple and cheap fix. 

Spoiler

 

 

9 hours ago, ApertureS said:

Just saying ‘the battery tests okay’ is not massively helpful as many will now skip over the battery without wondering it if it truly okay.

 

what kind of test was done? When was the test done? What equipment was used? What were the specific results of the test?

 

The problem is sporadic - I can go days with no issue, then suddenly it wont start even after a long drive. I have taken to turning off infotainment and turning lights to OFF instead of AUTO when shutting down.

First time it happened (after a 30min drive, failed to start) after gutting jump-start, I drove straight to my mechanic. He used this battery diagnostic kit that guided him through steps - at certain points he asked me to turn on lights and heating full blast..

His conclusion that the battery diagnostic seemed fine and battery seemed fresh and of a good brand. He noted that it was running ~13v was a bit odd.

13 hours ago, ords said:

After a long run, can you start the car or is the battery flat?

 

 

sometimes yes, sometimes no

16 hours ago, Warrior193 said:

Hello, welcome to the forum. If your battery tests as OK - and your alternator voltages look good, I'd suggest that there is something not 'going to sleep' correctly after you shut down.

Check the forum for parasitic drain on battery. The noisy fuel pump should not be the cause (unless it keeps running after engine shut down)

Were there any changes made to the vehicle around the time this problem started?  

Thanks for this, will check the forum for parasitic drain 

9 hours ago, @Lee said:

I doubt what I suggest is the cause but MkI Fabia's had a common fault where the alternator load sensor wire failed resulting in not keeping the battery charged sufficiently. It's worth considering as from memory it was a relatively simple and cheap fix. 

This is interesting, may explain why im seeing voltage jump from 12v - 14v while driving around

@9737u50 - varying alternator voltages are normal with the micro-hybrid energy system, with battery charging intended to be primarily from energy recuperation during coasting and braking. The battery will typically be charged to around 75-80% by the alternator using engine power - leaving capacity for energy recuperation.

Edited 9 December, 20232 yr by Warrior193
correction

A very good description, that should be a sticky because so many people are being duped into replacing perfectly servicable batteries though ignorance often that of a mechanic who they should be able to trust.

22 minutes ago, Warrior193 said:

@9737u50 - varying alternator voltages are normal with the micro-hybrid energy system, with battery charging intended to be primarily from energy recuperation during coasting and braking. The battery will typically be charged to around 75-80% by the alternator using engine power - leaving capacity for energy recuperation.

Very interesting, did not know the battery system was that smart!

OK, well I suppose i'm still in the dark. I will read up on this forum about parasitic drain and continue to monitor for anything unusual.


Another fact:

When I bought the car a year ago it had a brand-new battery installed, old battery was in the boot and seemed fine (reading 12v).

Dealer was unsure why new battery had been put in by previous owner.

Edited 9 December, 20232 yr by 9737u50

31 minutes ago, 9737u50 said:

When I bought the car a year ago it had a brand-new battery installed, old battery was in the boot and seemed fine (reading 12v).

Battery off load voltage is not a good indication of battery condition - an old battery that has high internal resistance can still read 12V off load but be unable to start the engine.

52 minutes ago, 9737u50 said:

Very interesting, did not know the battery system was that smart!

OK, well I suppose i'm still in the dark. I will read up on this forum about parasitic drain and continue to monitor for anything unusual.


Another fact:

When I bought the car a year ago it had a brand-new battery installed, old battery was in the boot and seemed fine (reading 12v).

Dealer was unsure why new battery had been put in by previous owner.

Was the old battery the same type and capacity as the one currently fitted?

There is an adaptation required in the BCM, ideally every time a battery is replaced - especially if the replacement is different from the original. Critically, is the present battery a EFB or AGM?

Edited 9 December, 20232 yr by Warrior193
extra question

2 hours ago, 9737u50 said:

Very interesting, did not know the battery system was that smart!

OK, well I suppose i'm still in the dark. I will read up on this forum about parasitic drain and continue to monitor for anything unusual.


Another fact:

When I bought the car a year ago it had a brand-new battery installed, old battery was in the boot and seemed fine (reading 12v).

Dealer was unsure why new battery had been put in by previous owner.

When the battery was fitted was it coded ? yes I know you will say you don't know well check if it is coded !

Also with your problems check the earths, on the Alternator side of things

1) Check battery has been coded in.  All VAG vehicles post 2013 needed this doing.

2) You need to get an amp-clamp meter.  Try latching the bonnet and locking the car.  Amp-clamp the battery and try and find out if the car goes to sleep.  It shouldn't draw anything more than 15-20mA when asleep.

3) Do a CCA test on the battery.  This will determine if you have a weak battery due to failing internals.  Try doing this after charging it up with a charger.  CCA value will be on the battery.

7 minutes ago, varaderoguy said:

All VAG vehicles post 2013 needed this doing

Only those with start/stop and its associated different battery types and charging system, I believe, which I don't think is all from that date.

Edited 18 December, 20232 yr by Breezy_Pete

11 minutes ago, Breezy_Pete said:

Only those with start/stop and its associated different battery types and charging system, I believe, which I don't think is all from that date.

You are right - generally those with auto-stop/start and AGM batteries needed to coding; but it was at that time to VAG required people to start coding in their batteries.  If an older style battery and no auto-stop/start, then no coding needed.