173 problems have been reported for the 2009 Audi A4. The following chart shows the 18 most common problems for 2009 Audi A4. The number one most common problem is related to the vehicle's air bags with 52 problems. The second most common problem is related to the vehicle's engine and engine cooling (50 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 2009 Audi A4 in the United States are 39,069 units [1]. If the total number of problems reported by Audi A4 owners in the last 15 years is 173, and the age of the vehicle is 15, the PPMY index can then be calculated as
PPMY Index = 173 / 39,069 / 15 * 1000 = 0.30.
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 2009 Audi A4 in 2009.
| Service Year | Number of Problems |
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| 2009 |
When making the decision between buying a new or used Audi A4, the following table can be used to compare the 2009 Audi A4 with the Audi A4 from other model years. Note that the number of problems reported for the 2009 A4 is 173 while the average number of problems reported for the 29 model years of the Audi A4 is 117.