# Vehicle Reliability Survey results -- Audi A6 (C5)



## mkaresh (Oct 26, 2005)

The latest results of the Vehicle Reliability Survey, based on owner experiences through the end of September 2008, have been released.
Audi A6 (C5) reliability results, in terms of successful repair trips per 100 vehicles per year:
2000: 131, about average, but very small sample size; based on other results, the actual repair rate is probably worse than average
2001: 184, worse than average, small sample size
2002: 140, worse than average, small sample size
Other years: insufficient data
Descriptions of all reported repairs have been posted to the site, for those interested in that level of detail.
Full set of results:
TrueDelta Vehicle Reliability Survey results


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## Snowhere (Jul 27, 2007)

*Re: Vehicle Reliability Survey results -- Audi A6 (mkaresh)*

Jezz, a sample size of 10 to 17 cars does not mean anything. Statistically speaking, if they sold 5000 A6, they sampled only 3/10ths of a percent of cars. I just pulled the 5000 # out of a hat, I have no idea how many cars were sold. It would be nice if they did use a representative sample so the info would mean something. It can't be too hard to do as most A6 sold new are most likely dealer maintained for the initial owner. Why they can't get into that info is beyond me. I was able to look up every used car I was looking at just by asking a dealer to look it up for me.


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## mkaresh (Oct 26, 2005)

*Re: Vehicle Reliability Survey results -- Audi A6 (Snowhere)*

A representative sample is very expensive, for three reasons:
1. Must buy the registration info
2. Registration info doesn't include email address, so must send paper surveys via snail mail
3. Must process paper surveys
You would not be willing to pay the resulting price for the results. Which is why no reliability survey that provides a useful amount of information to the general public uses a representative sample.
The number sold is not relevant to figuring out the required sample size. It's not even part of the statistical calculation. That said, 17 is too few to provide anything but a broad indicator. I start to see stable results around 25, and especially over 50. Which is doable--we have that many for dozens of other models. Just not this one yet.
Think of it this way: if you asked 17 people about their experience with a particular car, would you consider the information they provided of any use? How many decisions have you based on the experiences of fewer than ten people?


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## Snowhere (Jul 27, 2007)

*Re: Vehicle Reliability Survey results -- Audi A6 (mkaresh)*

Assuming the level of awareness I am sure the official group of 17 would be, I would not trust what they say about any car. Let's face it, most people out there have no clue how to maintain a car to keep problems from happening. A larger sample would, at least, average out the clueless with the enthusiast. What is the standard deviation on the information? I expect it to be pretty large. Nothing is worse then no information other then un-reliable information.


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## mkaresh (Oct 26, 2005)

*Re: Vehicle Reliability Survey results -- Audi A6 (Snowhere)*

We post the descriptions of all reported repairs. For the 2000 through 2002 A6 (first few dozen):
--heated seat element
--CV boot
--thermostat stuck
--tie-rod ends
--mass airflow sensor
--another CV boot
--front door pocket flaps broken
--yet another CV boot, and the joint
--fuel pump flange cracked
--wheel bearing
--another themostat stuck
--alarm sensor
--cam seals
--coolant auxiliary pump
--turbo bypass valve
--antenna amplifier wire
--coolant tank
--window guide broke
--EGT sensor
--ABS sensor
--coolant sensor
--yet another CV boot
--another thermostat
--another aux water pump
--another cam seals
--another coolant sensor
So, which of these repairs would have been avoided through proper maintenance?
I hear "if you maintain a car properly, you won't have problems" or "people who have problems just don't know how to maintain a car properly" all the time.
While there's no doubt that proper maintenance will help avoid major mechanical issues, one thing has been very clear from the data this survey collects: major mechanical issues are rare, and the great majority of the parts that do fail are not maintainable.
It's comforting to think that most and even nearly all repairs can be avoided through proper maintenance. But this theory is not supported by the data.


_Modified by mkaresh at 8:39 PM 11-22-2008_


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## Snowhere (Jul 27, 2007)

*Re: Vehicle Reliability Survey results -- Audi A6 (mkaresh)*

You raise valid points on the the listed repairs. I just do not see it as a representative sample and really do not feel it should be promoted as such. I am not knocking what you do, it just needs more info improve the certainty of the data. That and if the data was broken up by engine, the sample size would be even smaller.
Based on your list, my car must be the one of the many, you did not sample. With 89,000 miles on the clock, I had the cam seals replaced along with one tierod end. The po had the car serviced at the dealer and did not have any repairs that were not wear related. I did not have to replace the seals and the tierod, it just made sense as they were worn or crusty. That is the type of maintenance that tries to catch stuff before it wears out.


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## mkaresh (Oct 26, 2005)

*Re: Vehicle Reliability Survey results -- Audi A6 (Snowhere)*

You'll get no argument from me on the value of a larger sample size. If we had 100+ owners for every model year and engine, I wouldn't complain








My main disagreement is your implication that a result based on 17 or so responses is worse than no result at all. If you look over the current results, you'll find that even those with small sample sizes correlate with other studies much more often than they do not. On the site, we state the sample size in each case, so people can tell how precise the result is likely to be. A few are over 100, even 200 already. Unfortunately, no year of the A6 is yet among these. But it'll get there. The only question is not if, but how soon.
This is one of many cases in life where starting small and gradually improving is much more likely to lead to the desired goal than saying, "If the initial product isn't perfect, it's better to have nothing at all."


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## deucescorner (Jul 4, 2006)

This was my biggest fear in buying a C5, so far:
- left and right front axle
- rear bushing
- passenger side window regulator
- diverter valves
- valve seals
- cam seals


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