Emissions Test

It is often part of periodic inspection. Modern tests read OBD data. Diesels may get a smoke or particle test. After clearing fault codes or disconnecting the battery, the car must be driven until the readiness monitors are complete, otherwise it may fail. Some countries combine OBD checks with tailpipe measurements. Tampering with emission controls, such as removing a particulate filter, is illegal and is checked for during inspections.

Measurements or OBD checks show whether systems work.

Warning lights can fail the test. Incomplete readiness monitors can cause failure.