2004 Mercedes-Benz ML500 OBDII Drive Cycle Test Cost

An on-board Diagnostics II (OBD-II) drive cycle test refers to a functional set of steps that a driver must take in order for the vehicle to test itself for emissions related failures. They are called drive cycles because the vehicle must achieve several conditions in proper succession and for the proper duration. In other words, it must cycle through many different conditions required before it it will approve of the emissions related systems for the engine.

OBD-II vehicles, mostly 1996 and newer, have strict emissions guidelines imposed by state and federal laws, so the manufacturers are required to add some self-testing features into vehicles for compliance with emissions testing equipment. This self-testing protocol is basically a succession of steps beginning with things like cooling the vehicle, starting the vehicle, warming the engine, driving a particular speed for a set duration or distance, slowing, idling, etc. Once all of these conditions are met, the vehicle will understand whether the emissions related components are functioning properly, or if there is a failure somewhere in the system.

After a repair which illuminated the check engine light is complete, if a drive cycle needs to be completed to verify the repair, the check engine light will stay on, and the OBD-II trouble codes stored or pending will remain until the drive cycle is complete. Aside from this, when it comes time for emissions testing, the vehicle will not pass dude to monitors which are not ready for testing. This means the vehicle has not yet tested itself, so it cannot report this information to the testing equipment at the emissions testing facility. The real symptom here would be failure of an emissions test, or the check engine light will not turn off after a repair.

Depending on applicable local laws, this could be as urgent as every year, or once every several years. When the check engine light is on, it is always a good idea to have it diagnosed, however, nearly all vehicles with a system monitor which is not ready for testing due to an incomplete drive cycle test are not affected by this until emissions testing is at hand. If the vehicle does not require emissions testing, there is no reason to seek out performing a drive cycle test unless to verify a repair and reset the check engine warning light.

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.