Porsche 911 owners have reported a total of 94 problems for their cars built in the 17 model years listed in the chart below. The chart shows the number of problems reported across all service years for each given model year of the Porsche 911. The 1999 Porsche 911 cars have the most problems reported (12 problems).
The following chart shows the 16 most common problems for Porsche 911 cars. The number one most common problem is related to the vehicle's engine and engine cooling (37 problems). The second most common problem is related to the vehicle's equipment (12 problems).
It would not be fair to compare the Porsche 911 of an older model year to newer model years since older vehicles have been in service longer and thus are expected to have more problems. In order to compare the reliability across 911 model years, we use the PPMY index which is defined as the problems reported per thousand vehicles per Year. A smaller PPMY index indicates greater reliability of the given model year cars.
PPMY = P / S / Y * 1000,
where P = total problems reported during the life of a Porsche 911 model year; S = total units sold of the model year; Y = years since the debut of the model year (the age of the vehicle).
The results are shown in Table 3.