OBD II Readiness Monitors

Monitor Status

Monitor Status: Ready VS Not Ready

OBD II equipped vehicles follow standardized protocols when reporting monitor status to scan tools or emissions inspection devices such as the (NYVIP2) equipment. When a particular monitor is not applicable to the vehicle being tested, the monitor is reported as unsupported. The vehicle cannot report the results of this monitor simply because it does not exist. Most gasoline-powered OBD II vehicles have at least a few unsupported monitors. Unsupported monitors have no role in the overall readiness evaluation or the overall OBD inspection result.

Those monitors incorporated into the vehicle manufacturer’s emissions control design are referred to as being supported. Supported monitors need to be evaluated by the vehicle’s PCM during readiness monitoring. For most gasoline powered light duty vehicles, the common range of the number of supported monitors is six to eight. When the PCM successfully completes the execution of a particular monitor, the readiness system status will be reported as Ready or Complete. Once a monitor is set as Ready or Complete it will remain in this state unless diagnostic trouble codes (DTCs) are cleared by a scan tool or if the PCM’s short term memory is erased by a power failure (i.e., disconnecting the battery). Since the three continuous monitors are constantly evaluating, they will be reported as Ready all of the time. If testing of a particular supported non-continuous monitor has not been completed, the monitor status will be reported as Not Complete or Not Ready.

Just because the monitor status for a particular readiness monitor is Ready or Complete, this does not mean the PCM stops executing the monitor. Whenever the enabling conditions for a particular monitor are met, the PCM runs the monitor. If the monitor runs successfully or is interrupted nothing is changed by the PCM. But if a monitor executes and a fault is incurred, a pending code is typically set in memory. And if the fault continues to happen, the PCM illuminates the check engine light and DTC fault code is set.

In most cases to turn the check engine light off and reset the monitor status to Ready, the vehicle has to be repaired and the monitor needs to be run again.

New York has adopted the federal Environmental Protection Agency (EPA) guidance concerning readiness during OBD II inspections. A vehicle will fail the (NYVIP2) OBD II inspection if enough monitors are reported as Not Ready. Generally, OBD II vehicles from model year 1996 to model year 2000, inclusive, will fail if more than 2 monitors are set as Not Ready; while model year 2001 and newer vehicles will fail when more than 1 monitor is reported as Not Ready.

Any of the following may cause your vehicle to not be ready:

Disconnecting the battery for any reason. This erases the memory in the PCM, including stored fault codes and previous OBD monitor test results. It's like resetting the clock back to zero. Consequently, it may take several days (or even weeks) of driving before all of the monitors will run, allowing your vehicle to be tested.

Erasing stored codes with a scan tool. This also resets all of the monitors back to zero, so allow plenty of time for the monitors to run before driving back to the emissions test facility. If any of the erased fault codes reappear, it may prevent one or more of the monitors from completing.

Disconnecting sensors. This will prevent the monitors from running and will likely set one or more fault codes. Removing the catalyst converter. This is emissions tampering and is illegal for street-driven vehicles.