Audi A3: Problems with check engine light, engine running and misfiring

The alternator is new and the voltage is still too high.

(Translated from German)

Hello everyone, after replacing the alternator, the voltage is still too high when the engine is running. What could be the reason for this? After I deleted the fault memory, the engine ran very unevenly at the beginning, but only when I accelerated did it stay on and calm down after a while. Where does this come from? Greetings Niko

(Translated from German)

Hi Niko, if the voltage is still too high after replacing the alternator, it could be due to a faulty voltage regulator. Even though the alternator is new, the regulator could be defective. As for the uneven engine running, it could be due to a number of reasons such as a vacuum leak, dirty fuel injectors, or a faulty mass air flow sensor. I would recommend having these components checked. Please keep us updated on your progress. Do you have any other questions?

Hello, before I replaced the complete alternator, I first replaced the regulator on the old alternator, there was no change and then I installed a completely new alternator. There were two new regulators in use. Can't it come from somewhere else? Greetings Niko

(Translated from German)

Hi Niko, if you've already replaced the voltage regulator twice and the problem persists, it's possible that there's an issue with the wiring or a grounding problem. I would suggest checking the wiring from the alternator to the battery and the ground connections. Also, check the condition of the battery terminals and clean them if necessary. Please keep us updated on your progress. Do you have any other questions?

Hello, here is an update on the status. During the engine misfires or misfires, the message "Start Stop has been deactivated, please start the engine manually" appeared on the board computer from time to time. I then disconnected the plug responsible for the start/stop, which is next to the battery. Since then, the voltage is in the green range and there are no more interruptions when accelerating. Apparently the automatic start/stop system switched off the engine briefly when accelerating.....Now I have to keep looking for it.....When the plug is on, the old problems are also there.....Which control unit does this cable go to? Greetings Niko

(Translated from German)

Hello, Which plug did you disconnect exactly? Normally, the automatic start/stop function is controlled by the engine control unit itself. If present, the problem could also be with the battery sensor which monitors the battery. If this sensor has a problem or is defective, it could be sending incorrect values to the engine control unit, causing the battery voltage or the charging voltage of the alternator to be too high.

(Translated from German)

Hi Niko, the cable you disconnected likely goes to the battery sensor, which is part of the start/stop system. This sensor monitors the battery's state of charge and communicates with the engine control unit. If it's faulty, it could be sending incorrect information to the engine control unit, causing the high voltage and start/stop issues you're experiencing. I would recommend having this sensor checked or replaced. Please keep us updated on your progress. Do you have any other questions?