How to troubleshoot a faulty engine in an Audi A8?

My Audi A8 is experiencing engine issues, what are some steps I can take to diagnose and fix the problem?

First, check for any error codes using an OBDII scanner. If there are none, then it could possibly be a problem with the fuel pump or ignition system. Ensure the fuel pump is receiving power and check for any spark in the ignition system. If those seem fine, it could be a problem with the engine control module or sensors.

If your engine is cranking but not starting, it could be a sign of a weak or dead battery. Make sure to check the battery voltage and test the connections. It's also a good idea to check the air filter, as a dirty or clogged filter can also cause engine problems.

If there is a knocking sound coming from the engine, it may be a sign of low oil pressure or a problem with the bearings. Check the oil level and make sure it is at the recommended level. If it is low, add more oil and see if the knocking sound persists.