Last week, I repaired the first car on my own. It was a 2010 Audi A4L equipped with CDN 2.0T FSI engine and had about 10,000 miles on it. The problem was that the car battery drained very often, contributing to frequent engine failure.
According to the car owner, he had used a VAS 5054A to troubleshoot, but did not get anything, and the problem had happened for at least 6 times. Since it was impossible to drive the Audi to our auto repair shop, I used a Jump Start Emergency Charger to provide power for it, and the car could start smoothly then. Since the vehicle could start after connecting to the auto emergency charger, I was sure the battery was fine, which meant the problem was caused by electric leakage of one or more auto parts.
To troubleshoot the problem, I replaced a new battery and test the quiescent current when the car went into sleep. 45 minutes later, I noticed the number of the quiescent current jumped from 0.02A to 0.9A. I could determine there was electric leakage then.
The vehilce suddenly started to create strange sounds when I was about to carry out further diagnoses. I kept on working and pulled out its plugs one by one to check current change. When I pulleg out the plug connecting the radio, the current jumped into the normal range. That should be the problem.
So I replaced the raido control unit and restarted the vehicle a few hours later. The voltage was normal and the car could be started smoothly then. Although I forgot to use an OBD2 tool for help, I finally solved the problem on my own.