California’s BAR lets any one monitor stay incomplete on 1996 to 1999 gas cars, and the evaporative monitor on 2000 and newer ones.

The plain answer

California’s Bureau of Automotive Repair (BAR) defines readiness monitors as self-tests that the vehicle’s OBD system runs to verify emission control functionality. On the OBD test portion of a Smog Check, BAR lets any one monitor stay incomplete on a 1996 to 1999 gas vehicle. On a 2000 and newer gas vehicle, BAR names the evaporative system monitor. Diesel vehicles follow other limits, shown in the table below.

Incomplete means a self-test has not finished. After a repair or a battery event, CARB says that does not necessarily mean anything is wrong with the car.

The sections below reproduce BAR’s table with its footnotes, list the monitors, and quote what BAR, CARB and EPA say about resetting and completing them. Our readiness overview gives the shorter version.

How many may be incomplete in California

BAR’s On-Board Diagnostic Test Reference lists the number of incomplete readiness monitors allowed to pass the OBD test portion of a Smog Check inspection. The table reproduces it and adds a plain-words column.

BAR’s footnotes and revision history add four details.

• “Gas” includes gasoline, propane and natural gas (CNG, LNG, LPG).
• BAR’s inspection ignores the misfire, fuel and comprehensive component continuous monitors during an OBD test on “gas” vehicles.
• BAR marks the limits as implemented on May 4, 2015, and marks the 2007 and newer diesel entry as implemented on July 5, 2023. Before that date the entry for those diesels was “any two”.
• BAR’s revision history lists version 8.6, dated March 5, 2026, as the latest. We read the page on October 22, 2026.

For 2000 and newer gas vehicles the table names one monitor, the evaporative system, and no other. The ignored continuous monitors in the second detail still apply, and model years 2026 and 2027 follow a separate rule, covered next.

The newest model years

BAR’s list of vehicles of interest has its own rows for model years 2026 and 2027. For all vehicles of those years it says the vehicle has OBDonUDS, which 13 CCR §1968.2 references as SAE J1979-2, and that “DAD 1.0 units will not communicate with OBDonUDS vehicles.” A DAD is the data acquisition device that retrieves OBD II information from the vehicle for BAR’s inspection computer. BAR’s instruction for these model years reads “Cal-VIS software programmed to skip the OBD test until DAD 2.0 units are BAR certified.” Cal-VIS is the BAR software that conducts Smog Check and Vehicle Safety Systems inspections. The monitor limits above belong to the OBD test, and BAR says its software skips that test for these cars until DAD 2.0 units are certified.

BAR also lists specific makes and models with known pattern issues in the OBD test portion. It says that in most cases its inspection system is programmed to accommodate a vehicle with a design anomaly, and that in other cases the vehicle may require repair. BAR describes its reference as including vehicles whose inspection has been modified through “modified pass/fail standards, disabled test modules, or OBD data collection.” One entry, for example, tells inspectors that the system will ignore the EGR/VVT monitor. Check your car against BAR’s list.

What a readiness monitor is

BAR calls readiness monitors “self-tests performed by the vehicle’s OBD system to verify emission control functionality.” California’s OBD rule for 2004 and later vehicles requires the system to indicate “complete” or “not complete” for each installed monitor since the fault memory was last cleared, with one section for vehicles using SAE J1979 and another for vehicles using SAE J1979-2. EPA’s 2001 report calls that status a readiness code and describes it as a flag that differs from a trouble code because it records whether a given monitor has run.

On what BAR calls OBD Classic vehicles, a scan reads the status through Mode 01 PID 01. BAR says that request returns the warning-light status, the diagnostic trouble codes and the monitor status. BAR’s reader specification gives UDS OBD II vehicles a separate list, with Service 22 identifiers instead. Our PID guide explains how parameter requests work. The same BAR page sets separate standards for the warning light, for communication and for permanent trouble codes. Our check-engine-light guide covers the lamp.

Which monitors exist

EPA’s 2001 report says the OBD system monitors “up to 11” emission control subsystems with continuous or periodic tests. BAR’s own vehicle list also refers to 11 readiness monitors. EPA names them as follows.

EPA says a scan can show each monitor as ready, not ready, or not applicable, and that not applicable means the vehicle lacks that component monitor. For vehicles using SAE J1979, California’s rule for 2019 and newer vehicles names the gasoline entries Catalyst, Evaporative System, Secondary Air System, Fuel System, Oxygen Sensor, Oxygen Sensor Heater and EGR/VVT, and says the Misfire and Comprehensive Component entries always indicate “complete”. For diesel vehicles it names NMHC Converting Catalyst, NOx Converting Catalyst, Misfire, Fuel System, Exhaust Gas Sensor, EGR/VVT, Boost Pressure Control System, NOx Aftertreatment and PM Filter. Vehicles using SAE J1979-2 have their own list in section (g)(4.1.2).

What resets a monitor and what completes it

BAR says readiness monitors “must be rerun after a repair activity like disconnecting a vehicle’s battery or replacing a defective emissions component.” CARB gives a recently repaired fault and a dead, disconnected or replaced battery as causes of incomplete indicators. For vehicles using SAE J1979, California’s rule for 2004 and later vehicles says each monitor except the entries that always read “complete” must indicate “not complete” whenever fault memory has been cleared or erased by a means other than those that section (d)(2) allows. It also says normal key-off shutdown may not cause that status. Our freeze-frame guide covers what else clearing can erase.

Completion takes driving. BAR notes that drive cycles “require the vehicle experience specific operating conditions: speed, temperature, pressure, engine load, etc.” A vehicle may never complete a monitor “until a thorough diagnosis and repair of components enabling the monitor to run is performed.” BAR says some owner’s manuals contain driving procedures, but “usually this drive cycle information is only available to the OEM or found in repair industry service literature.”

If a Smog Check reports incomplete monitors

CARB’s fact sheet, dated September 19, 2019, gives owners this guidance.

1. Owners who fail Smog Check because of incomplete readiness indicators should drive their vehicle as they normally do for about a week or so, CARB says, to set the indicators to “complete.”
2. If a recently disconnected or replaced battery most likely did not cause the incomplete indicators, or if the vehicle is not driven regularly, CARB says the owner may wish to seek repair technician help in setting readiness.
3. A technician can access technical information from the vehicle manufacturer and may advise specific driving patterns. The technician may also operate the vehicle, most likely on a dynamometer in the shop, to set the monitors. A scan tool shows which monitors have not completed.

CARB’s fact sheet says too many incomplete indicators mean the vehicle “has not been operated enough since the on-board memory was last cleared”, and that this “does not necessarily mean that anything is wrong with your car”. EPA’s 2001 report says that in such a case the vehicle’s emissions status is officially “Unknown”.

Where this guide stops

• Other states. EPA says vehicle testing requirements “vary across the country”. EPA’s rule at 40 CFR §51.357(a)(5) says that once OBD testing and repair are mandatory, a 1996 or newer vehicle “shall be rejected from testing” if a scan reveals a “not ready” code for any component. A state may choose instead to reject 1996 to 2000 vehicles only if three or more codes read “not ready”, and 2001 and later vehicles only if two or more do. BAR’s table sets California’s limits.
• Other tests. BAR’s table covers the OBD test portion. CARB’s 2019 fact sheet says Smog Check inspections for 2000 and newer vehicles are “now primarily based on an inspection of the OBD II system” and that tailpipe testing is no longer required for them. It says 1996 through 1999 gasoline vehicles receive both an OBD inspection and tailpipe testing, and that 2000 through 2007 medium-duty vehicles with federal-only certified OBD systems may require both.
• Your drive cycle. The documents we read give no single driving pattern for every car. BAR says that information is usually only available to the manufacturer or found in repair industry service literature.
• Change. BAR revised the diesel limit in 2023 and its vehicle list in 2026. Read the current BAR page before you test.

Axlyne’s boundary

Axlyne does not perform a Smog Check, certify readiness or compliance, interpret local rules, or predict a station’s decision. It records supported standard generic OBD2 responses through a separate compatible ELM327 adapter. Support varies by vehicle, adapter and phone.

Official sources

• California Bureau of Automotive Repair, On-Board Diagnostic Test Reference
• California Air Resources Board, On-Board Diagnostic II systems fact sheet, September 19, 2019
• California Code of Regulations, Title 13, §1968.2, section (g)(4.1) readiness status
• U.S. EPA, Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program, EPA420-R-01-015, June 2001
• U.S. EPA, 40 CFR 51.357, test procedures and standards for inspection and maintenance programs
• U.S. EPA, Overview of Vehicle Inspection and Maintenance (I/M) Programs, October 2021
• California Bureau of Automotive Repair, Data Acquisition Device Specification, October 2023