Under the OBD II standard the vehicle’s computer monitors the emission systems in two ways.
The first, is referred to as “Continuous” where major emission causing faults such as Engine Misfire and incorrect Air/fuel mix are continually monitored.
The second is referred to as “Non-continuous”. This is where checks are made only once each warm up cycle.
Each time the engine is started, the computer checks components such as the Oxygen sensor, catalytic converter and other engine systems are functioning correctly. If a fault is detected the MIL is illuminated indicating that the vehicle needs attention.
If the condition is intermittent and the faulty system operates normally, the MIL will turn off after the vehicle has operated through three warm-up cycles, but the Diagnostic Trouble Code will remain in the computer memory for a set period.
If the fault does not reoccur within 40 drive cycles, the code will be automatically erased but will remain logged in the computer memory as a history code.
