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Hi Everyone.

My 2018 TT TFSI 1.8 has recently been tripping its alarm randomly but very occasionally. I obviously want to diagnose the issue and sort it out so that the neighbours don't get their pitchforks out [again]...

I'd read that random alarm events can be caused by low battery voltage. I've checked the battery voltage without the engine running, which is around 12.4v but running, it only reaches around 12.6v - where I'd expect something between about 13.5v and 14.5v. The output voltage of the alternator is about the same as the battery at about 12.6v when running. I don't want to assume that the alternator is at fault as I've heard that the age and the performance of the battery will influence the voltage at which the alternator charges the battery and so it could just be that the battery needs replacing [and re-coding]. I've also read that the alternator will only charge at it's maximum voltage when the car is coasting or during braking. My tests have all been completed when the car is either off or idling.

I'm not getting any low-charging warning lights. I've yet to run VCDS to see if that reveals anything but will do so over the weekend.

In the meantime, do any of you have any experience of this symptom? Any experiences and guidance would be really appreciated.

Thanks everyone.
 

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Only suggestion I have is check the voltage the alternator is producing at @ 2000 rpm with a significant load ie switch on lights,headlights,heated rear screen,air con full blast . . .etc would expect increase voltage from alternator to show
 
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