Where this data comes from
Anyone can file a vehicle safety complaint with NHTSA, the US National Highway Traffic Safety Administration. NHTSA publishes them, and uses patterns in them to open investigations that sometimes become recalls. This tool pulls those public complaints live and groups them by the system the owner picked.
How to read the counts
Complaints are unverified, and counts depend on how many cars were sold and how many owners bother to file. A popular commuter car will have far more complaints than a rare sports car, even if the sports car is less reliable. Compare the shape of the list (which system dominates) more than the total, and read the owners' descriptions: five people describing the same failure at the same mileage tells you more than a big number.
What complaints can't tell you
Enthusiast cars often have their best-known problems missing from NHTSA entirely, because those problems aren't safety issues or owners fix them without filing anything. Forum knowledge fills that gap, which is what our per-car reports are built from.