A car diagnostic test can identify issues in a vehicle's engine, transmission, brakes, exhaust system, ignition coils, fuel injectors, coolant, and throttle body. The test uses specialist software and diagnostic tools to analyze data from the car's built-in processors and internal sensors. Common problems that can be detected include the vehicle's emission levels, faulty powertrain control modules, idle speed stress, and small transmission issues. The diagnostic test helps determine the source of problems in order to save both time and money on repairs.