Drive Cycle
A specific sequence of driving conditions required for the vehicle's computer to run its internal OBD-II readiness monitors.
An OBD-II drive cycle is a specific sequence of vehicle operation designed to allow the engine control unit to run and complete its diagnostic self-tests (known as readiness monitors). These monitors evaluate emissions control systems, including the catalytic converter, EVAP system, EGR valve, oxygen sensors, and misfire detection.
A drive cycle typically requires a combination of cold starting, idling, city stop-and-go driving, and highway cruising at constant speeds (such as driving at 55 mph for 15 minutes). If the battery is disconnected or if codes are cleared, all readiness monitors are reset to 'not ready.' The vehicle will fail state emissions inspections until the drive cycle is completed and the monitors show 'ready.'
If a component is failing, the drive cycle will allow the computer to detect the issue, trigger the check engine light, and store a DTC. Some monitors, like the EVAP monitor, have strict parameters (such as the fuel tank being between 1/4 and 3/4 full and the engine sitting overnight) and can be difficult to complete without following a precise manufacturer drive cycle guide.