Volvo S90 owners have reported a total of 52 problems for their cars built in the
5 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 Volvo S90.
The 1998 Volvo S90 cars have the most problems reported (38 problems).

Table 1. Total number of problems by model year for Volvo S90

The following chart shows the 17 most common problems for Volvo S90 cars.
The number one most common problem is related to the vehicle's service brakes, hydraulic
(12 problems).
The second most common problem is related to the vehicle's equipment (7 problems).

Compare Reliability Across Model Years Using PPMY Index

It would not be fair to compare the Volvo S90 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 S90 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 Volvo S90 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.

Table 3. Use PPMY Index to Compare Reliability Across S90 Model Years