UK-POLOS.NET - THE VW Polo Forum

Hi all.

Joined here in hope someone can save me any more unnecessary spending!

So, I've a 2013 1.2 TDI Bluemotion which has been trouble free for 4 years ownership. Used for work commuting, mainly at night, the car has started throwing battery light on at start up intermittently. Monitoring this with a obd app on phone and a multimeter, when the problem occurs, the alternator hasn't kicked in, Volts reading between 12 and 11.6. The light never stays on when alternator kicks in normal at start up. So far when fault occurs the alternator has always kicked in a few minutes later taking volts up to 14.5, but with driving mostly at night, involving a long motorway journey, I'm nervous about it not kicking it at some point!

The car has had both new alternator and battery, fault is exactly same now as before either replaced, so both of these can be eliminated and reving doesn't encourage alternator to kick in either. Only other noticeable difference when fault occurs is higher than normal tick over at just over 1k, and stop start error flashing across display. No other light shows, no fault codes showing, or at least not on my simple obd app.

Anyone had or heard of similar issues? Been told battery sensor on negative connector worth a look but I'm clueless on this tech, this being my first issue I've had with stop start tech fitted car ect!

Any help or ideas would be much appreciated.

Due to the previous problems, it is assumed that when installing the new alternator and battery the following operations were carried out:
- Cleaning and inspection of battery cables and terminals.
- Cleaning and inspection of the 2-pin connector - wires of the Battery Monitoring Control Module.
- Electronic Adaptation of the new battery.
- Cleaning and inspection of the alternator connector, wire, and terminal.
- Condition of fuse SA1.
- Condition of the poly-v belt and tensioner.

It is possible that the lack of charging (when it happens) is due to the battery monitoring control module is failing, but maybe you may find something in the above because charging is fine when a certain operating temperature/time is reached...

ciclo wrote: Sun Oct 22, 2023 6:14 am Due to the previous problems, it is assumed that when installing the new alternator and battery the following operations were carried out:
- Cleaning and inspection of battery cables and terminals.
- Cleaning and inspection of the 2-pin connector - wires of the Battery Monitoring Control Module.
- Electronic Adaptation of the new battery.
- Cleaning and inspection of the alternator connector, wire, and terminal.
- Condition of fuse SA1.
- Condition of the poly-v belt and tensioner.

It is possible that the lack of charging (when it happens) is due to the battery monitoring control module is failing, but maybe you may find something in the above because charging is fine when a certain operating temperature/time is reached...

Thanks for reply pal.

Yeah, working through those options currently, still got battery sensor on negative terminal to try and my main hope.... issue gotten worse over last day or so, with most starts once warm resulting in alternator not kicking in for several minutes now, and in one instance never cut back in whatsoever!

Will update when/if find the cause.

Thanks again for response

6R CFWA Bluemotion.

Maybe try unplugging the small connector from the battery module - this will always inhibit auto Stop, but with it disconnected you will be able to "see" if it changes the charging behaviour from engine start. Really just in a bid to dismiss or consider it is the battery module that is faulty, these replacement battery modules cost roughly £100 by the way.

Edit:- that small battery module connector needs the locking element pulled outwards first, then the connector will unplug - and obviously the reverse when re-connecting it.

This does sound a lot like being a wiring issue, and at least the earlier models of TDI Polo/Ibiza/Fabia did end up fracturing some of their small cables, like the excitation cable to the alternator and/or the load sense cable to the alternator, and that tended to happen below the engine<>gearbox join where there is a connector.