OBD Monitors and Testability Issues

OBD Monitor Readiness

check engine lightReadiness monitors are self- tests performed by a vehicle’s on board diagnostic (OBD) system to verify emission control functionality.

While most vehicles complete the various self tests during normal driving, achieving monitor readiness in a few types of vehicles is more difficult due to the vehicle design requiring unusual operating conditions or due to the fact that the owner never drives the car in the necessary operating mode.

Monitor completion is also dependent on properly functioning components, so a vehicle may never complete a monitor until a thorough diagnosis and repair of affected components is performed.

Readiness monitors must be rerun after a repair activity like disconnecting a vehicle’s battery, clearing diagnostic trouble codes,  or replacing a defective emissions component.

OBD Test Monitor Readiness Standards
(Implemented May 4, 2015)
Model Years Fuel Type total Incomplete Monitors allowed
1996-1999 Gas* Any One
2000 and newer Gas* Evaporative system
1998-2006 Diesel Zero
2007 and newer Diesel Any two
*”Gas” includes gasoline, propane, natural gas (CNG, LNG, LPG)

OBD Monitor Readiness Testability Issues

Some vehicle models are known to have issues that interfere with the successful completion of OBD readiness monitors.  The State of California Bureau of automotive repair maintains a list of these vehicles and specific remedies, if known, that can assist a motorist in completing monitors.  In some cases repairs may be required, and in others test equipment is programmed to ignore some or all readiness monitors on affected vehicles.

To learn more about OBD readiness monitors and testability issues, please download the Smog Check OBD Reference from the Bureau of Automotive Repair website.

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