2015 Polo 1.2TSI 110PS 6C charging voltage changed to over 14V at all times!

RUM4MO

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As per the title line, for some sensible/stupid reason, I bought a cheap plug in DVM that I fit into the power socket in the centre console so that I can monitor the charging voltage, I have used this for maybe the past 9 > 18 months. Actually I had checked this charging level a lot earlier, just after the car to understand how it worked by using a made up lead and DMM, but buying this plug in cheap DVM made it easier to do.
Since the beginning of using that DVM I've got to understand when the battery actually gets charged and when it doesn't along with typical voltages, typically 12.5V when the engine is powering the wheels, and 13.7V when on the overrun - so that sounds okay and keeps the battery within its intended state of charge which I think is round about 80% max.
Over the past week, the voltage readings have changed to a constant 14.8>14.9V at all times after the initial few seconds at 12.?V, ie both when the car is driven and when on the overrun.
I checked these voltages with another and trusted DMM both at the power socket and across the battery and also to chassis, and I get the same values.
I unplugged the battery dongle and that seems to have reduced the charging voltage to 14.1>14.5V.
I checked the car with VCDS and there are no faults logged - except for the battery dongle being open circuit while it was unplugged, the logged car battery usable charge is presently 36Ah from a 59Ah EFB, battery charge level 78% and battery rest voltage 12.5V. VCDS obviously also shows no thermal/mechanical/electrical issues with the alternator.
So, any guesses as to what has changed - is it the battery (original) that has reached a turning point in its health as far as the car's smart charging system is concerned?
If so, maybe this need to react by whacking the charging to a constant 14.8/14.9V is what leads to the demise of these EFB when most people will not have any idea of what is going on relative to charging levels, maybe if I'm correct, I should see this as being the point at which I change this battery for an AGM version and recode the battery section in CAN Gateway controller.
I just hate it when I seem to be the first to report something!!!
 

Crasher

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Circa 14.8v is spot on for EFB and AGM batteries, in the olde days I would discourage customers who wanted gauges as before the car was fine and after they just obsessed about the readings… it why VAG decided to make the coolant temperature gauge read 90 all the time, to stop people obsessing about the minutiae of the readings, only problem is it didn’t work!
 

RUM4MO

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Crasher thanks for that reply, yes gauges can be handy and/or not. Lots of folks on the SEAT and Skoda forums for equivalent models to Polo rage a lot about not having temperature gauges and I sort of sympathise with them - although the "analogue" temperature coolant gauge is actually receiving digital data and only responding to quite "big" changes.

My problem with this Polo is, I've checked the typical charging voltages soon after buying this car new, same for my 2011 S4 really just to get an idea of when they did charge and what the voltage values were, in both cars roughly the mid 12.?sV during the non charging when under power and roughly 13.7 on the overrun. One car has an EFB and the other an AGM battery.
This change to constant 14.?V only started with the Polo over the past week and that DVM has been plugged in for between 9 > 18 months - the change in behaviour, in my case is quite a bit, and that concerns me and no doubt will bother me until I can get to the bottom of it or my wallet!
As it stands, the average fuel usage should be increased though determining that while the outside temperature is dropping will not be easy.

I've always owned and run cars that had coolant temperature gauges - except for a month when I bought a used 1972 maybe L reg Escort 1300 DL van, but I soon sorted that after a trip to a scrappy to get the instrument binnacle from a similar aged Escort XL, the van already had the sensor and wiring in place.
 

RUM4MO

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Well one thing that I failed to mention yesterday was, as a final attempt to try something else, I changed the serial number of the battery and ran the engine for maybe a couple of minutes - nothing seemed to change, but at least everything stayed working though the charging voltage stayed at 14.8/14.9V. Today we used the car and initially nothing had changed, I drove roughly 12 miles at roughly 50 MPH and then back into 30 MPH zones and then I noticed that the charging voltage had returned to behaving as it had done from when the car was new until a week ago. On the way home, same sort of journey the charging voltage alternated from 12.6 etc V to 13.7 ect V - and a constant 14.6V.

So, one way of looking at this is that the BMS is attempting to optimise the charging of this battery which it assumes is another battery, and in changing the charging profile, it can end up for a short period "sorting out" this charging issue - which if true, does indicate that this battery has reached a point where the BMS can not keep it working/charged/charging in a way that behaves as a Blue Technology car should.

A few, for me, good points as it looks like the alternator electronics pack is not dead/faulty as that when dealing with solid state devices tends to change from working to faulty, with no chance of self repairing, same for the battery dongle, BMS part of the controller and wiring, maybe a simplistic approach, but what I see does follow that logic.

So, putting my money where my mouth is, I stopped off at Costco and grabbed a Bosch S5A08 this is the next size up of battery and an AGM, Costco did not stock any of the S5A05 027 size of battery, so I'll need to fit the new battery tray and insulator that I bought a while ago as I had discovered that this bigger size of battery is sometimes cheaper than the smaller 027 size, probably this 096 size is more popular. Hopefully I'll sort this battery changing later this week as I've yet to change an O-ring seal in a water pipe on my S4 and refill it with G12EVO.
 

Crasher

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The old and defunct British Battery Manufacturers Association number 096 is now a very common size, we are seeing a LOT of problems with Yuasa 9000 series batteries including one today (a job from another garage) as every single one we fitted has failed, we will now only fit Varta. Also we are seeing a lot of battery monitoring units fail, we wanted to change the one on the above mentioned car but due to huge demand there is no UK stock… which is telling!
 

RUM4MO

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By "battery monitoring units" do you mean the "battery wiring set" that has the current measuring resistor as part of it - or the CAN - Gateway controller? I think that I've noticed quite a lot of these small VW Group cars needing to get that "dongle" replaced under warranty, ie in very early life.
I had considered "taking a stab" at this at the beginning and just replace the "battery wiring set" that contains the current measuring resistor that is connected to the -VE pole of the battery, but then I think that I bumped into one of your older postings that mentioned a price like roughly £69 from a year ago - so as I had observed an immediate change in the charging voltage, okay still constant, when I disconnected the lead from that device, I considered that it had still some functionality, so I opted with replacing the battery which by all accounts do not last that long on these Stop/Start models.

Luckily for me I have in effect bought a Varta battery , though a battery made for Bosch by Varta so plastics in Bosch colours.

Yuasa batteries, I've never ever bought one, but as they are Japan owned, I think, I had always thought that they should be high quality and so very reliable - then I started reading lots of stories of people hopping into Halfords and buying a new battery for their car - and either needing to get it replaced or get let down very badly, so I'd never consider them now for a car battery.
 

Crasher

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It is the little three wire device on the earth lead lead, it has quite a lot of data and communicates with the alternator on a LIN BUS line and then to the Body Control Module. I was working from home remotely on a late Caddy yesterday which was having voltage issues and I recommended they replace the Yuasa 9000 series battery with a Varta AGM and the battery monitor but they called me back later and told me the monitor is on back order as the demand is so high.
 

RUM4MO

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Thanks again for that, being maybe a "doom and gloom" or "preparing for the worst" person (!!), I was concerned that this issue I have would end up at the alternator or the controller!

Buying a new earth/dongle if need be does not concern me - if and when I find I still have an issue and VW Group manage to keep up with demand. The one fitted to that Polo is I think a Lear branded one made in Spain - if there are "good" ones and "known bad" brands supplying VW Group.

Any repeat of this after I fit this new battery and I'll swop the old battery back in until I can buy a new monitor unit.
 

RUM4MO

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Bother I wrote another posting then thought that I had ended up duplicating it, deleted!

Anyway what I was posting was that this Polo is starting to behave a bit better, after I changed the battery serial number, but not as "well" or the same voltages and patterns of changing voltage that it did about 2 weeks ago before it changed to constantly charging at 14.8/14.9V at all times.
I ended up buying a new battery monitor ordered in by my VW dealer parts dept, it is again a LEAR Spain part manufactured in 2020 and labelled up by VW Group as 04/07/2021, so it looks like there has not been "a run" on this version of battery monitor. I'll fit this some time after I replace the battery, but I'm temped to leave things as they are for the time being while keeping a close eye on the voltage reading and reacting if things look like "going bad" - I should stick VCDS on it and check to see if any of the "re-reg'd old battery" stats are changing. The smart money is surely on my sorting this out before the temperature drops much more as working with metal tools in a cold garage is not much fun! I will post any updates as they happen and not just disappear into the ether after asking for help!
 

RUM4MO

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I've not replaced anything yet as I'm interested to see where this is going, and hopefully do something before things get worse or as soon as it reverts back to a constant 14.9V charging. Presently the charging is being controlled and charging voltage does vary, though typically will spend a lot more time charging at the overrun types of voltage. The battery seems to be getting kept at a lot higher state of charge than it was prior to this. I've checked using VCDS and the total energy throughput stuff has been reset by that serial number change - which is to be expected, just a pity that I had not looked far enough down the list to find that field BEFORE changing the serial number though!!
More updates when things change.
 
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