Audi A6 C6: Transmission Diagnostic Guide

This article applies to the Audi A6 C6 (2004-2010).

Transmissions, a once relatively simple component of the automobile, have become highly sophisticated pieces of technology in recent years. As automakers add gears and technology to automatic boxes, the number of and types of problems have evolved as well. While most transmissions will last a long time under reasonable use and with proper maintenance, this isn't always the case with some cars. One of which is the Audi A6 C6, a car that is so notorious for CVT transmission issues that it settled a lawsuit with around 64,000 folks. If you are one of the unlucky masses facing transmission issues with your A6, keep reading and we'll walk you through the diagnostic process.

Step 1 – Change your transmission fluid and filter

Sometimes a simple service will correct the issue.

Many transmission issues can be corrected by simply changing out the transmission fluid and filter. While manufacturer recommendations for this service range from 50,000 to 100,000 miles, it's often the cheapest (at least by Audi standards) and easiest route. Surprisingly to many, lagging and noisy shifts between gears tend to go away once this service is completed. Plus, it gives you the opportunity to inspect the fluid and your trans case for metal shavings, which could indicate a much bigger problem. Be sure and clean your pan thoroughly when performing this job.

If changing your fluid and filter doesn't solve the problem, move on to step 2.

Step 2 – Check for codes and software updates

Sometimes the problem can be identified using VAG-COM.

If you have access to a VAG-COM cable or can borrow (or rent one), you can check the system for faults. Standing for "Volkswagen Auto Group Computer," VAG-COM is pretty much a prerequisite to owning a modern VW or Audi product, as it will allow you to go inside the brain of the car. One of the most common faults that can trigger a code is the torque converter, which can cause hesitations or slipping between gears while accelerating (a common issue with these cars).

There is also a TSB for automatic equipped Quattro cars relating to the chirping, hooting, and squeaking noises experienced when shifting between 3rd and 4th gears. This problem can be solved with a simple software update that can be performed at the dealership, along with a fluid flush.

In some cases, problems with slipping under acceleration have been solved with an adaptive transmission learning reset, which wipes the memory and resets it to factory specs. This can be completed at the dealership or with a VAG-COM cable.

If you don't have any codes or a software issue, move on to step 3.

Step 3 – Car is stuck in park or 4th gear

Your car might be in "limp" mode or the brake light switch could be faulty.

If your car is stuck in 4th gear, it means you are in limp mode. If all the segments of your transmission range indicator in the instrument cluster are lit up, a critical malfunction has occurred. The car will drive forward in 4th gear only, and reverse will work. If the TR indicator doesn't light up at all, there is an issue with the TCM. If none of the forward gears work but reverse does, you have a serious transmission problem that will probably require a rebuild (if you're lucky) or replacement.

If your car is stuck in park and won't shift out, check your brake light switch. Look under the ashtray and you'll see a hole, into which you can stick something to disengage the lock (white button) that prevents the car from going into drive when it's in park. You can also turn the ignition on and hold the shifter in between drive and neutral, then try to start the car.

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