Timeline of events
About 8 weeks ago - Occasionally EPC light would come on and car would go into limp mode sometimes associated with EML and sometimes with a stop/start error on MFD but never any error codes. A restart would clear fault.
About 6 weeks ago - Fitted new battery which seemed to fix the problem for a few weeks until
A few days ago - Problem re-appeared with same symptoms. Battery voltage was down to 12.3 so charged battery overnight and it was ok for a couple of days until
Yesterday - Problem re-appeared but this time would not clear on a restart. Also error code was generated saying open circuit injectors 1 and 4. AA man turned up and checked some connections which seemed OK but this action seemed to cure the problem.
Today - Checked voltage of battery which was 12.4 with engine off. Started car and revved it but voltage did not change. No lights on dash and no error codes.
Is this all caused by one fault somewhere or do I have several faults? Do I have a faulty alternator, a faulty battery, bad wiring or some ecu problem?
Car is 2017 Yeti 1.2TSI on 44,000 miles.
Any advice would be gratefully received.

The battery voltage should rise to about 14.5 volts once the alternator is being turned by the engine. If it's still sitting at 12.4 it's very likely that the alternator is not charging. If your car is new enough to have a smart alternator, diagnosis is not quite so clear cut, but I would still expect to see a noticably raised battery voltage immediately after starting. You should see some kind of warning light on the dashboard.

The car can run with a failed alternator for an hour or two, provided you don't switch on big loads like headlights and heater fan etc, but eventually the battery will be flattened and the engine will stop. So if you wan't to drive to a nearby garage you should be OK. If you can fully charge the battery with a mains charger first, so much the better.

I have done some further testing of the alternator and it is a smart one. It only puts out power as required. Starting the car and just revving the engine did not initiate any power output and voltage stayed at 12.6V but switching the headlights on and voltage went to 13.3V. Heated screen and seats pushed it up to 14.9V. So it seems that the alternator is not dead. I don't know if it should start charging sooner. Maybe it would if the battery voltage fell below 12.6V.

Hello, welcome to the forum.

At 2017, your Yeti would have smart alternator and automatic idle stop (Stop/Start) - does that operate correctly - do you normally use it?

At 12.6 volts, your battery is approx. 85% charged - which is a little above the level that the smart alternator limits its output to allow for energy recuperation.

Try leaving the headlights on for about 10 minutes with the engine off, then check the battery terminal voltage with the engine idling.

It is possible that the voltage sensor wire to the alternator has a bad connection - this appears to be relatively common problem reported on the forum.

Edited 6 March, 20251 yr by Warrior193
added information

'Smart alternator', what a nonsense!

Do they actually save anything, I very much doubt it but if they do it must be all but unquantifiable.

Sounds like a cure looking for a disease!

Helps with fuel economy/CO2 rating during Type Approval testing, primarily.

Charge management with EFB/AGM batteries, which mustn't be overcharged, too.

Edited 7 March, 20251 yr by Breezy_Pete

22 minutes ago, Breezy_Pete said:

Helps with fuel economy/CO2 rating during Type Approval testing, primarily.

Charge management with EFB/AGM batteries, which mustn't be overcharged, too.

Point 1 - yes, and at least it's not got an ISG/BSG 'very smart!' Generator as they go wrong(!)

Point 2 - use a ctek trickle charger which has an AGM mode

Both from experience 👍

Edited 7 March, 20251 yr by Prezafab

3 hours ago, Prezafab said:

Point 1 - yes, and at least it's not got an ISG/BSG 'very smart!' Generator as they go wrong(!)

Point 2 - use a ctek trickle charger which has an AGM mode

Both from experience 👍

Pete was referring to the alternator charge management levels while driving.

Edited 7 March, 20251 yr by Warrior193
typo