Help Needed: Resolving DTC 03157 and Overvoltage Issues in Audi Q3

Start by checking the battery and alternator voltage output to ensure they are within the normal range. Overvoltage can often be caused by a faulty voltage regulator in the alternator. If the voltage is too high, it could lead to the issues you're experiencing. Let us know what you find, and we can guide you further.

Thank You for your quick answer, I will check.

Check the battery terminals for any corrosion or loose connections as well. This can sometimes cause voltage irregularities. Let us know if you find anything unusual or if the problem persists after checking the alternator and battery.

I check alternator charging, with engine running it is 12,92 V.

The alternator output seems low, as it should typically be around 13.5 to 14.5 volts when the engine is running. This could indicate a problem with the alternator itself or the voltage regulator. I recommend having the alternator tested and possibly replaced if it's faulty. If you have any further questions or need more assistance, feel free to ask.

I tested charging by the electrician and he says probably its ok, because there is computer monitoring of this charging process. Have to be something other problem.

Consider inspecting the ground connections and wiring harnesses for any signs of damage or poor connections, as these can also cause voltage issues. If the problem persists, it might be beneficial to have a professional perform a more in-depth diagnostic to pinpoint the exact cause. Let us know how it goes or if you have more questions.