Does California DMV Check OBD2? Understanding Smog Check and OBDII Testing

For California drivers, the Smog Check is a familiar, if sometimes dreaded, part of vehicle ownership. Ensuring your car meets California’s stringent emissions standards is not just about legal compliance; it’s a crucial step in maintaining air quality and public health. A common question among vehicle owners is, “Does California Dmv Check Obd2?” The answer is a resounding yes. The California Department of Motor Vehicles (DMV), through its Bureau of Automotive Repair (BAR), heavily relies on On-Board Diagnostics II (OBD2) systems as a cornerstone of the Smog Check program for most vehicles.

This comprehensive guide will delve into the specifics of how California’s Smog Check program utilizes OBD2 systems. We’ll explore what the OBD2 check entails, what pass/fail standards are in place, and what you need to know to ensure your vehicle successfully navigates this critical inspection. Understanding the role of OBD2 in California’s Smog Check is essential for every car owner in the state.

What is OBD2 and Why is it Important for California Smog Checks?

OBD2, or On-Board Diagnostics II, is a standardized system built into most cars and light trucks manufactured since 1996. Its primary function is to monitor the performance of your vehicle’s engine and emission control systems. When the OBD2 system detects a problem that could increase emissions, it illuminates the Malfunction Indicator Lamp (MIL), commonly known as the “Check Engine” light, on your dashboard. Simultaneously, it stores Diagnostic Trouble Codes (DTCs) which pinpoint the nature and location of the issue.

California’s adoption of OBD2 checks into the Smog Check program represents a significant advancement in emissions testing. Prior to OBD2, Smog Checks relied heavily on tailpipe emissions testing, which could be less effective at identifying certain types of emission control system failures. OBD2 testing offers several key advantages:

Comprehensive System Monitoring: OBD2 monitors a wide array of emission-related components and systems, including the catalytic converter, oxygen sensors, evaporative emissions system, and more. This provides a more holistic view of a vehicle’s emissions performance.
Early Problem Detection: OBD2 can detect emission problems early on, often before they become severe enough to noticeably impact vehicle performance. This allows for timely repairs, reducing harmful emissions and potentially preventing more costly repairs down the line.
Standardized Diagnostics: The standardized nature of OBD2 means that any certified Smog Check station can access the same diagnostic information from your vehicle, ensuring consistent and reliable testing.
Efficiency and Speed: OBD2 testing is generally faster and more efficient than older methods, reducing the time required for a Smog Check inspection.

In California, OBD2 testing is not just a component of the Smog Check; for many vehicles, it is the primary emissions test. This means that if your vehicle fails the OBD2 portion of the Smog Check, it will automatically fail the entire inspection, regardless of tailpipe emissions readings (if performed).

California Smog Check OBD2 Pass/Fail Standards: Key Components

The California Smog Check OBD2 test evaluates several key areas to determine if your vehicle passes or fails. These areas are designed to ensure that your vehicle’s emission control systems are functioning as intended and not contributing excess pollution. Here’s a breakdown of the critical components of the OBD2 Smog Check in California:

1. Readiness Monitors: Ensuring System Self-Testing

Readiness monitors are self-tests performed by your vehicle’s OBD2 system to confirm the functionality of various emission control components. Think of them as internal health checks. These monitors run automatically under specific driving conditions and verify systems like the catalytic converter, oxygen sensors, evaporative emissions system, and EGR system are working correctly.

For a vehicle to pass the OBD2 Smog Check, a certain number of these monitors must be in a “ready” or “complete” state. California’s standards allow for a limited number of incomplete monitors, acknowledging that some vehicles may have difficulty completing all monitors under normal driving conditions. The allowable number of incomplete monitors depends on the vehicle’s model year and fuel type:

Model Year	Fuel Type	Number of Incomplete Monitors Allowed to Pass OBD Test
1996-1999	Gasoline (including propane, natural gas)	Any one
2000 and newer	Gasoline (including propane, natural gas)	Evaporative system
1998-2006	Diesel	Zero
2007 and newer	Diesel	Particulate Filter and Non-Methane HydroCarbon (NMHC)

Important Notes on Readiness Monitors:

“Ready” vs. “Not Ready”: A “ready” monitor indicates the self-test has run and passed. A “not ready” or “incomplete” monitor means the test has not yet been completed.
Driving Cycles: Completing readiness monitors often requires specific “drive cycles” – a set of driving conditions (speed, acceleration, temperature, etc.) that must be met for the self-tests to run. These drive cycles can sometimes be found in the vehicle owner’s manual or service information.
Monitor Reset After Repairs: Whenever you disconnect your vehicle’s battery or have emission-related repairs performed, the readiness monitors are typically reset to “not ready.” You will need to drive your vehicle through the appropriate drive cycles to allow the monitors to complete before a Smog Check.
Continuous Monitors: The misfire, fuel system, and comprehensive component monitors are continuous monitors and are always running when the engine is operating. These are generally ignored during the OBD test for gasoline vehicles in California.

If your vehicle has more incomplete monitors than allowed based on the table above, it will fail the OBD2 Smog Check.

2. Malfunction Indicator Lamp (MIL) – The “Check Engine” Light

The Malfunction Indicator Lamp (MIL), or “Check Engine” light, is a critical indicator of your vehicle’s emissions health. The California Smog Check OBD2 test includes a check of the MIL’s behavior in two key states:

Key On, Engine Off (KOEO): When the ignition key is turned to the “on” position but the engine is not running, the MIL should illuminate briefly. This confirms the MIL is functional and not burned out.
Key On, Engine Running (KOER): Once the engine is started and running, the MIL should turn off. If the MIL remains illuminated while the engine is running, it indicates an emission-related fault.

MIL Pass/Fail Standards:

Pass: MIL illuminates during KOEO and turns off during KOER.
Fail: MIL does not illuminate during KOEO, or MIL remains illuminated during KOER.

Any MIL illumination during the KOER portion of the test is an automatic failure of the OBD2 Smog Check.

3. Communication: Establishing a Link with Your Vehicle’s Computer

For the Smog Check station’s equipment to assess your vehicle’s OBD2 system, it must be able to communicate with your car’s computer. The communication check ensures that the Smog Check analyzer can successfully connect to your vehicle’s OBD2 port and retrieve the necessary data.

Communication Pass/Fail Standards:

Pass: The Smog Check analyzer (BAR-97 or OIS system) successfully communicates with the vehicle and retrieves the required data (typically data from OBD addresses Mode $01 PID $00 and Mode $01 PID $01).
Fail: The Smog Check analyzer cannot establish communication with the vehicle’s OBD2 system.

Reasons for Communication Failure:

Damaged OBD2 Connector or Wiring: Physical damage to the OBD2 port under your dashboard or the associated wiring can prevent communication.
Aftermarket Stereo or Accessories: Improperly installed aftermarket electronics can sometimes interfere with OBD2 communication.
Vehicle Computer Issues: In rare cases, a problem with the vehicle’s engine computer (ECM) or other control modules can prevent communication.
Incorrect Protocol: Older Smog Check equipment (DAD 1.0 units) may not be compatible with newer vehicle communication protocols like OBDonUDS (OBD over Unified Diagnostic Services).

If your vehicle fails the communication portion of the OBD2 Smog Check, you will need to diagnose and resolve the communication issue before it can pass.

4. Permanent Diagnostic Trouble Codes (PDTCs): Addressing Persistent Issues

Permanent Diagnostic Trouble Codes (PDTCs) are a type of DTC introduced to address the issue of drivers clearing regular DTCs just before a Smog Check to temporarily hide emission problems. PDTCs are similar to regular DTCs, but they cannot be cleared using a scan tool or by disconnecting the vehicle’s battery. PDTCs can only be cleared by the vehicle’s OBD2 system itself, after it verifies that the underlying fault has been corrected and the system is functioning properly over multiple drive cycles.

California’s Smog Check program includes a check for PDTCs for 2010 and newer vehicles.

PDTC Pass/Fail Standards (2010 and newer vehicles):

Fail: The vehicle has any PDTCs stored in its computer.
Pass: The vehicle has no PDTCs stored.

Important Notes on PDTCs:

PDTCs and MIL: A vehicle can fail for a PDTC even if the MIL is not currently illuminated. This is because a PDTC indicates a past emission issue that has not yet been fully resolved by the vehicle’s self-monitoring system.
Warm-up Cycles and Mileage Exception: There is an exception for PDTCs if the vehicle has completed at least 15 warm-up cycles and been driven at least 200 miles since its OBD information was last cleared. This exception is designed to accommodate situations where a PDTC might linger temporarily after a repair.
Known PDTC Issues: California BAR recognizes that some vehicles have issues with improperly clearing certain PDTCs. For a list of these “Permanent Diagnostic Trouble Code Vehicles of Interest,” refer to Section E of the original document. In some cases, BAR-OIS will ignore specific PDTCs for these vehicles.

The PDTC check is a crucial part of ensuring that emission repairs are not just temporary fixes and that vehicles are genuinely addressing underlying emission problems.

5. Modified Software: Upholding Emission Control Integrity

California takes a firm stance against tampering with vehicle emission control systems, including modifications to the vehicle’s software. The Smog Check program includes a check for modified software in the vehicle’s engine control module (ECM).

Modified Software Pass/Fail Standards:

Fail: The vehicle is identified as having illegally modified software that affects emission controls.
Pass: The vehicle’s software is either OEM-approved or CARB-approved (California Air Resources Board).

Modified Software Check Details:

CARB Executive Orders: Software updates or modifications that have been approved by CARB through an Executive Order are permissible and will not cause a Smog Check failure.
Illegal Modifications: Software modifications that bypass or defeat emission controls are illegal and will result in a Smog Check failure.
Inspection Report: If a vehicle fails for modified software, the Vehicle Inspection Report (VIR) will indicate “Modified Software” as the overall inspection result.
Restoration and Retest: To pass a Smog Check after failing for modified software, the vehicle must be restored to an OEM-approved or CARB-approved software configuration. Retesting can be done at any licensed Smog Check station, unless BAR directs the vehicle to a Referee or STAR station.

The modified software check aims to prevent individuals from circumventing emission regulations through software tuning and ensures that vehicles operate with emission controls as originally designed or with CARB-approved modifications.

Vehicles of Interest: Known OBD2 Testing Issues in California Smog Checks

California BAR maintains lists of “Vehicles of Interest” related to OBD2 Smog Checks. These lists highlight specific vehicle makes, models, and years that may have known issues with the OBD2 test portion of the Smog Check. These issues can range from communication problems to difficulties in completing readiness monitors or false MIL illumination.

These lists are divided into:

OIS Vehicles of Interest (Section D of original document): This section focuses on gasoline and flex-fuel vehicles (model year 2000 and newer) and diesel vehicles (model year 1998 and newer) that have known OBD2 testing issues during an OIS (Smog Check Inspection System) inspection. The table provides details on the specific issue, the cause and possible remedy, and instructions for Smog Check inspectors on how to handle these vehicles.

Common issues listed in this section include:
- No OBD Communication: Certain models may fail to communicate with the Smog Check analyzer due to design anomalies or software issues.
- Incomplete Readiness Monitors: Some vehicles may have difficulty setting certain readiness monitors due to software errors or design characteristics.
- OBD Test Incompatibility: Older Smog Check equipment might not be fully compatible with newer vehicle communication protocols.
- False MIL Illumination: In some cases, vehicles may falsely illuminate the MIL during the OBD2 test due to software sensitivities.
For many of these “Vehicles of Interest,” the OIS system is programmed to accommodate the known issue, often by ignoring certain monitors or adjusting test parameters. In other cases, the vehicle may require a software update or repair to address the underlying problem. Smog Check inspectors are instructed to follow specific procedures outlined in the table for these vehicles.
Permanent Diagnostic Trouble Code Vehicles of Interest (Section E of original document): This section lists vehicles known to have problems with clearing certain PDTCs. For these vehicles, BAR-OIS may ignore specific PDTCs during the Smog Check. This list primarily includes vehicles from manufacturers like Audi, Chrysler, Dodge, Freightliner, Jeep, Mercedes, Ram, and Volkswagen. The table specifies the make, year, model, engine, the PDTC issue, the cause/remedy, and instructions for inspectors. Often, the remedy involves a software reflash from the dealer.
BAR-97 EIS Vehicles of Interest (Section F of original document): This section addresses vehicles from model years 1996-1999 that have monitor readiness issues during a BAR-97 EIS (Emission Inspection System) inspection. For these older vehicles, the BAR-97 EIS is often programmed to ignore readiness status due to design anomalies that make it difficult for these vehicles to complete all monitors. The table lists makes and models from BMW, Chrysler, Dodge, Eagle, Ford, Hyundai, Infiniti, Kia, Lexus, Mercedes-Benz, Mitsubishi, Nissan, Plymouth, Saab, Subaru, Toyota, VW, and Volvo.

Why are these “Vehicles of Interest” lists important?

For Smog Check Technicians: These lists provide essential guidance for inspectors, helping them to correctly test and interpret results for vehicles with known OBD2 quirks.
For Vehicle Owners: Knowing if your vehicle is on one of these lists can help you anticipate potential issues during a Smog Check and understand why your vehicle might be treated differently during the inspection process. If your vehicle is listed, it’s advisable to review the table to understand the specific issue and any recommended actions (e.g., dealer reflash).

It’s important to note that these lists are updated periodically by California BAR as new information becomes available. Always refer to the most current version of these lists for the most accurate information.

Preparing Your Vehicle for an OBD2 Smog Check in California

To increase your chances of passing the OBD2 Smog Check in California, consider these preparation steps:

Address the “Check Engine” Light: If your “Check Engine” light is on, have your vehicle diagnosed and repaired by a qualified mechanic before going for a Smog Check. A lit MIL is an automatic failure.
Complete Necessary Repairs: If you know of any emission-related problems or have received warning lights in the past, address these issues proactively. Proper maintenance is key to passing a Smog Check.
Allow Readiness Monitors to Complete: If you’ve recently had your battery disconnected or emission-related repairs, drive your vehicle for a sufficient period and under varied driving conditions to allow the readiness monitors to complete. Avoid short trips; longer drives with varied speeds and some highway driving are generally recommended. Consult your owner’s manual or a trusted mechanic for specific drive cycle recommendations for your vehicle if needed.
Check for Recalls and Technical Service Bulletins (TSBs): See if there are any open recalls or TSBs related to emissions for your vehicle make and model. Manufacturers sometimes issue recalls or TSBs to address known emission issues, often involving software updates. Performing these updates at a dealership before your Smog Check can prevent potential failures.
Ensure Your OBD2 Port is Accessible: Make sure the OBD2 port under your dashboard is easily accessible and not obstructed by any objects.
Consider a Pre-Smog Check: Some auto repair shops offer pre-Smog Check inspections. This can be a worthwhile investment, as they can identify potential issues that might cause your vehicle to fail the official Smog Check, giving you time to address them.
Be Aware of “Vehicles of Interest” Lists: Check if your vehicle is listed in any of the “Vehicles of Interest” sections in the original document. Understanding potential known issues for your vehicle can help you and the Smog Check technician navigate the process more effectively.

By taking these proactive steps, you can significantly improve your vehicle’s chances of passing the California OBD2 Smog Check and contribute to cleaner air in the state.

Conclusion: OBD2 Checks are Central to California’s Smog Check Program

In summary, yes, California DMV does check OBD2 systems as a critical part of the Smog Check program. For most vehicles, the OBD2 test is the core of the emissions inspection. Understanding the components of the OBD2 test – readiness monitors, MIL, communication, PDTCs, and modified software – is vital for California vehicle owners.

By ensuring your vehicle’s OBD2 system is functioning correctly, addressing any emission-related issues promptly, and preparing your car for the Smog Check, you can confidently navigate this requirement and contribute to California’s ongoing efforts to improve air quality. If you have any concerns about your vehicle’s OBD2 system or its ability to pass a Smog Check, consult with a certified mechanic specializing in emission control systems.

Remember, a passing Smog Check is not just about legal compliance; it’s about responsible vehicle ownership and protecting the environment we all share.

The OBD II port is typically located under the dashboard on the driver’s side of the vehicle. This port allows communication with the vehicle’s computer for diagnostic and Smog Check purposes.

The Malfunction Indicator Lamp (MIL), or “Check Engine” light, illuminates when the OBD II system detects an emissions-related problem.