OBD II Emissions Monitors – UnderhoodService
Connect with us
Close Sidebar Panel Open Sidebar Panel

Emissions

OBD II Emissions Monitors

OBD II is primarily emissions-driven and will set codes anytime a vehicle has a fault that may cause emissions to exceed federal limits by 1.5 times. It doesn’t necessarily mean the vehicle has a real emissions problem. Many times it does not. But, if the nature of the failure is such that it might cause emissions to rise, OBD II will set a code anyway. That is why some states are allowing motorists to opt for a second-chance tailpipe test if their vehicle fails an OBD II test. In many instances, the vehicle will pass the tailpipe test.

Advertisement


OBD II is primarily emissions-driven and will set codes anytime a vehicle has a fault that may cause emissions to exceed federal limits by 1.5 times. It doesn’t necessarily mean the vehicle has a real emissions problem. Many times it does not. But, if the nature of the failure is such that it might cause emissions to rise, OBD II will set a code anyway. That is why some states are allowing motorists to opt for a second-chance tailpipe test if their vehicle fails an OBD II test. In many instances, the vehicle will pass the tailpipe test.

Click Here to Read More
Advertisement

OBD II Emissions Testing: Is Your Car Ready?
One of the EPA requirements for using a plug-in OBD II check in lieu of a tailpipe test is to make sure the OBD II system is ready and has run its system monitors. Some vehicles have readiness issues when it comes to setting all the OBD II monitors.

When OBD II runs a self-check on a particular component or system, it lets you know by setting readiness flags, which are displayed on your code reader or scan tool. If OBD II has run all the available monitors and finds no faults, the MIL remains out and the vehicle passes the emissions test. But if all the required monitors have not run, the vehicle can’t be given an OBD II test. The motorist must drive the vehicle and come back again, or take a tailpipe test if that is an option.

Advertisement

If OBD II detects a fault when running a monitor, the setting of a code may prevent the remaining monitors from running. A bad or slow oxygen sensor, for example, will prevent the catalyst monitor from running. Getting all the monitors to run can be tricky on some vehicles. Each monitor has certain operating requirements that must take place before the self-check will run.

To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no “universal” drive cycle that will guarantee all the monitors will be set and ready.

Advertisement

Some vehicles require very specific drive cycles (called “drive traces” if you perform them on a road simulator or dyno) to activate certain self-checks like the catalyst and EVAP monitors.

If you are checking an OBD II system and discover that one or more of the monitors have not run, it may be necessary to test drive the vehicle to set the remaining monitors.

An OBD II drive cycle is not just turning the ignition key on and off or starting the engine. A drive cycle requires starting a cold engine and driving the vehicle until the engine reaches normal operating temperature. The next drive cycle doesn’t begin until the engine has been shut off, allowed to cool back down and is restarted again.

Advertisement

On some vehicles, the drive cycle also includes the cold soak time between trips. On some vehicles, the EVAP monitor won’t run unless the vehicle has not been run for eight hours. There is no way to bypass or get around such requirements, so you have to do whatever the system requires. And if that means waiting, you have to wait.

Other faults can cause a monitor from completing. A faulty transmission shift position sensor can prevent the EVAP monitor from running. Also, communication issues that prevent the modules that share vehicle speed can also prevent a monitor from completing.

Advertisement
Click to comment
Connect
UnderhoodService