255 problems have been reported for the 2005 Audi A4. The following chart shows the 19 most common problems for 2005 Audi A4. The number one most common problem is related to the vehicle's exterior lighting with 96 problems. The second most common problem is related to the vehicle's air bags (55 problems).
In our research we use the PPMY index to compare the reliability of vehicles. The PPMY index of a certain model is defined as the problems reported per thousand vehicles per Year. The total sales of the 2005 Audi A4 in the United States are 47,280 units [1]. If the total number of problems reported by Audi A4 owners in the last 21 years is 255, and the age of the vehicle is 21, the PPMY index can then be calculated as
PPMY Index = 255 / 47,280 / 21 * 1000 = 0.26.
For more information, refer to this page: A study of reliability comparison across Audi A4 model year vehicles.
The following chart shows the number of problems reported during each of the service years since the debut of the 2005 Audi A4 in 2005.
| Service Year | Number of Problems |
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| 2026 | |
| 2025 | |
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| 2005 |
When making the decision between buying a new or used Audi A4, the following table can be used to compare the 2005 Audi A4 with the Audi A4 from other model years. Note that the number of problems reported for the 2005 A4 is 255 while the average number of problems reported for the 29 model years of the Audi A4 is 127.