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Your Burning On-Board Diagnostics Questions, Answered
5 minutes with CARB’s Fred Garza

Posted: March 1, 2022

As the mobility industry progresses toward a more environmentally friendly future, emission monitoring and regulations are only going to get more robust.

Understanding the on-board diagnostics (OBD) system’s functions and capabilities is becoming increasingly important, but as regulatory and standards requirements evolve, so do questions around these technologies.

We asked SAE International collaborators for their most pressing questions around what’s new in OBD and tapped Fred Garza, OBD Branch, Emissions Certification and Compliance Division for California Air Resources Board (CARB) to share his expertise.

Q: OBD systems are complex and appear to be required for non-emissions related components/systems on the vehicle. For example, why would my door ajar switch require OBD monitoring?

A: That’s a great question! In general, the OBD system needs to monitor emissions components/systems and detect malfunctions when certain emissions thresholds are exceeded. So how does a door ajar switch get involved? It could be for any number of reasons. For example, monitoring would be required if the door ajar switch is used to enable an OBD monitor, e.g., a cold start catalyst heating monitor, or if it leads to an emissions-increasing default action, e.g., the vehicle’s control system shuts off the engine stop-start system when a malfunctioning door ajar switch is detected. Although a vehicle component/system may appear to be non-OBD relevant at first glance, further review of how the component is integrated into the OBD system and emission controls may prove otherwise!

Q: California adopted an OBD-only inspection and maintenance (I/M) program for light and medium duty vehicles a few years ago and is planning a heavy duty I/M program in the near future. Why did California move away from tail-pipe emissions based I/M inspections and does OBD really help reduce emissions?

A: The new heavy duty I/M program is very exciting, and we’ll will be sharing details during the CARB Regulatory light duty OBD update and heavy duty OBD update presentations at the next On-Board Diagnostics Digital Summit-Europe in March 2022. California is moving away from tail-pipe emissions based I/M inspections because OBD II was initially designed as an I/M tool. Compared to tail-pipe based I/M, OBD offers more comprehensive fault detection capability and provides for less expensive, faster and more convenient testing. The OBD system can also alert vehicle owners of emissions faults as soon as the fault occurs and at emissions levels lower than the measurement capabilities of tail-pipe I/M devices, which helps reduce emissions.

Q: Passenger cars have emissions and diagnostic requirements that require owners to repair failures that can increase emissions - do motorcycles have similar diagnostic requirements?

A: Yes, California-certified motorcycles will require an OBD system in the near future! CARB is working on a proposal to require OBD for motorcycles tentatively starting with the 2024 model year. The plan is to harmonize with Euro 5 OBD requirements, initially, with additional requirements added later in the program. Be sure to check out our CARB Regulatory light duty OBD update and heavy duty OBD update presentations for additional details!

Q: After a code clear, my I/M inspection was a fail. Why did I fail if the MIL was off?

A: In order to run a successful I/M program, emissions faults on the vehicle have to be detected, which require OBD monitors to run and complete prior to an I/M inspection. Readiness status is an important feature of the OBD system that communicates “completion” status of specific OBD monitors (e.g., if they have run and completed) to the I/M inspector. After a code clear, this readiness status is cleared, thereby preventing the I/M inspector from determining whether an emissions fault exists on the vehicle, even though the MIL is off. The vehicle should fail the I/M inspection until the OBD monitors run and the OBD system communicates a “complete” readiness status to the I/M inspector.

Want to learn more about the latest regulatory and standards requirements, new legislative policies, industry drivers, and new and emerging technologies around OBD? Garza and his colleague Sam Bailey, Air Resource Engineer in the Diesel OBD Branch at CARB, will have a lot more to say during their upcoming talks at SAE’s On-Board Diagnostics Digital Summit-Europe (OBD-EU).

Join us at OBD-EU, March 15-17, online and on-demand, to hear from CARB, the European Commission, Vehicle Emission Control Center, and major industry vehicle manufacturers and suppliers. Register here.