Audi A4 cars are so well build, that it's practically impossible to encounter any kind of problems with a new A4 car. Nevertheless, exceptions happen. Problems may appear when you are driving reckless or when you take no care of your car. If you add time to that mix, you will definitely get an Audi A4 with minor problems that can become annoying (or even expand) if you don't fix them soon. I will start with the problems that I've encountered in my Audi, and I will add problems encountered by other users, along with a way of fixing them.
Audi A4 - common problems and fixes
1. The sensors
If you have an older Audi A4, at one point you can expect to have a faulty sensor. I had my ABS break sensor to fail, and when I pressed the break pedal, the ABS activated by itself, no matter the speed or conditions. That was really annoying. I finally got the car to a service and they fixed the problem with minor tweaks. Other CTS sensor fails could cause more fuel consumption, random misfire or other malfunctions. The common fix for these issues is to use a new green top sensor (CTS).
2. The window
On old Audi A4 models, you can expect the window regulator (or a piece of it) to fail at some point. The fix may include changing the full regulator, or just the window regulator plastic (which is way cheaper). In both cases, you need to strip the door panel down, and that's a difficult job to do. If you hear strange noises when you use an electric window, you can expect the regulator to fail pretty soon. In order to avoid this, you can use that window less. But, eventually, it will fail, so be prepared for it.
3. Electrical components
Electric failures are sometimes encountered in Audi A4 cars: the brake lights could stay on, the trip display can act strange, the power window motor could fail, a door speaker might crack. It's better to acknowledge these issues and try to fix them before they will expand and create even more problems. Keep your car in good health
4. Starting problems
If the Audi doesn'r start, and when you turn the key there is no "movement" from the car, you have a dead battery, a bad starter or a bad electric connection from the battery to the car. Check the battery cables, and check the electric power at the starter with a measurer while asking someone else to switch the key. If the power is there, but the car won't start, you will probably have to replace the starter.
5. Water leak inside the cabin
This was probably the worst problem I had with my A4 car. One day, out of nowhere, water was under my front seats. The problem: under the battery, there is a pipe (like a sink) that allows the water gathered from the windows to flow down to the ground. Because of leafs and everything that gets stuck there, sometimes the pipe gets clog, and the water has nowhere to go. So, it uses other orifices and holes. Some of them are going straight to the cabin. So, be sure to keep the area under the battery as clean as possible, and check it from time to time. In order to have access to it, remove the batter and open the two screws under the batter holder.
6. No heat from the vents
If the motor is on and everything seems ok, but you get no heat from the vents, you should check the fluid level. The common repair is to replace an O-ring piece that's found under the intake manifold. It's a common TBS problem encountered in A4 cars.
7. Auxiliary fans problems
Auxiliary fans can act crazy sometimes, staying on or off as they please. Usually, the problem is caused by a CTS sensor fails or the fan control module. You can try to replace the sensors by yourself, but it's probably better to have the car diagnosed by a dealer.
8. Transmission/oil leak
If your car is loosing oil or a strange liquid, you are probably having a leak somewhere. I had an oil leak in my A4 because of a loose connector, and I had transmission oil leak because of a broken pipe. Try to identify the problem by yourself, and go to an authorized service for a fix. The connector was pretty cheap, and if you're on a tight budget you can get those parts from a second-hand dealer.
9. Side mirror or navigation selector knobs
This knobs are made of cheap plastic, and after extended use, they might fail. The navigation selector could pop off in some cases. The replacements are not that expensive, and you can replace them by yourself. Check on youtube for a repair tutorial.
10. Headlights flickering
This happens mainly with Audi A4 cars that have Xenon lamps. Before going to a service with it, you can try to swap the faulty bulb to the other side. If the flickering continues, you have a bulb that needs to be changed. If there is no flickering, you probably have an electric problem with your faulty side of the car.
Bonus:
Strange/stinky smell in the cabinIf you experience strange smell in the A4's cabin, then you probably need to replace the air filter. If the problems persists after the filter replacement, you may experience water leak under the seats, and you need to fix it. Also, you need to clean the carpet under the seats, because the carpet is impregnated with stinky water, causing the awful smell.
