Emissions test facilities often request the owner of the vehicle drive the vehicle for an arbitrary amount of miles to pass an emissions test. This is typical when a drive cycle needs to be completed because at some point during that range, the vehicle should complete the test. This is so because the drive cycles are designed to reflect normal driving under various conditions. However, when drive cycles do not complete with normal driving, the technician has two options. They must diagnose the issue, or attempt the drive cycle. If the drive cycle will not complete, diagnosis of the failed monitor (system check) will need to be completed because vehicles will allow themselves to retest instead of fail. Diagnosis will follow a simple path since the monitors that were not ready will point to specific components or sets of components.

Before driving a vehicle for a week, we recommend obtaining the service manual in order to find the exact parameters of the OBD-II drive cycle test needed to set the monitors which are not ready or reset the check engine light. This will avoid lots of unnecessary driving, fuel costs, and wasted time. Also, it will allow the owner to understand exactly what is needed, and permit them to correct their mistakes instead of returning to the emission testing center for another fail.

OBD-II drive cycle tests are not designed to correct any issue. If a drive cycle is properly completed, and monitors still will not set (become ready), the vehicle likely has an issue. Likewise, if attempting to reset a check engine light after a repair is completed, this warning light will only turn off and stay off when the repair and drive cycle test have been properly completed.

Anyone can do a drive cycle test, but it may be difficult in high traffic areas. It is best to take the vehicle to a low-use area where the vehicle can meet all necessary conditions to pass the OBD-II drive cycle test. A scanner will be needed to verify that all of the emissions monitors are set (ready), and that no pending or stored codes remain on the powertrain control module. Since many shops will not offer a drive cycle test, the likelihood of the owner conducting the test is very high, even if they are unaware that they are conducting the test.