California rules set onboard diagnostic road map for EVs

WASHINGTON — As California goes forward with a plan to phase out sales of new gasoline-fueled cars and light trucks, the state's air regulators are seeking to ensure their battery-powered replacements are just as durable, reliable and repairable. It's a move likely to set the industry standard for electric vehicles.

Last year, the California Air Resources Board adopted a set of requirements that add transparency and uniformity to EV diagnostic data.

One key component is a requirement to provide drivers with an easy-to-access display of the battery's state of health and charging speed. It also guarantees independent repair shops have access to the same repair information and tooling as franchised dealer networks.

"There are certain things that right now are tracked on electric vehicles, but they're probably not tracked in a way that is comparable across manufacturers," said Anna Wong, manager of zero-emission vehicle regulations at CARB's Advanced Clean Cars branch. "This includes everything from the state of health of the battery to how the vehicle keeps track of its charging ability — how much charge it's able to accept at a given time."

Starting with the 2026 model year, ZEVs, including plug-in hybrids, must be equipped with a standardized data set and diagnostic connector that can be accessed using a generic hand-held scanner, much like the onboard diagnostic system II that's used for internal combustion engine vehicles.

Previously, EVs did not have onboard diagnostic monitoring or standardized data requirements, in large part because they have no tailpipe emissions. The CARB regulation, however, requires standardized data reporting for various aspects of the battery, charging system and propulsion-related parts such as the electric motor.

"You want to be able to take it into a repair shop," Wong told Automotive News. "You want to be able to access information about the vehicle with a scan tool. That is going to now be available on ZEVs."

The data standardization requirements are part of CARB's Advanced Clean Cars II regulation, which calls for ZEVs and plug-in hybrids to make up 100 percent of new-vehicle sales by the 2035 model year. It's also included in CARB's "ZEV assurance measures," which aim to reduce complexity and provide consumers with a more consistent ownership experience.

California adopted the regulation in 2022 but is still waiting for the EPA to grant a waiver under the Clean Air Act. At least seven other states have adopted the Advanced Clean Cars II program.

The California regulation is "the first step in the road map for OBD-like requirements for EVs," said Rob Weiss, who chairs an SAE International committee working on diagnostics for EVs.

Under the California regulation, certain functions and data — such as vehicle speed, odometer reading, state of charge, and minimum and maximum cell voltage — must be accessible by a scan tool "without the use of any vehicle manufacturer-specific, user-specific or tool-specific registration, authentication, authorization, login, password, certification or other mechanism that can be used to restrict or limit user or tool access for any other reason."

Requirements such as a consumer-facing battery health display also are tied to CARB's battery and propulsion-related parts warranty rules. For the 2026-30 model years, for example, CARB is requiring an eight-year or 100,000-mile warranty for any battery that falls below 70 percent of its state of health. In the 2031 model year, the warranted state of health increases to 75 percent.

EVs make up almost 8 percent of new-car sales today. But that's expected to grow dramatically if an April EPA vehicle emissions standards proposal is adopted. The EPA projects the regulation could push EVs to 60 percent of new-vehicle sales by the 2030 model year and 67 percent by 2032.
The EPA has not proposed adopting CARB's data standardization requirements for ZEVs. However, it did propose a battery state-of-health monitor that differs in some technical ways from CARB's requirements, according to the Alliance for Automotive Innovation, which represents most major automakers in the U.S.

The alliance said it wants battery durability and state-of-health requirements that align with international standards for consistency in monitor design and display.

"The way we've approached this is to get behind regulations that give consumers of new or used ZEVs everywhere the best tool to understand how their battery is functioning — in real time," Michael Hartrick, the alliance's senior director of energy and environment, said in a statement. "We've stressed the importance of consistency between EPA and CARB and ultimately globally … to further reduce complexity and costs to consumers."

CARB also wants consistency and has urged the EPA to adopt its suite of ZEV assurance measures, including the data standardization requirements.

"They have not pushed for those data standardization requirements yet," Wong said. "They could go further in making sure that consumers have a replacement to their gasoline vehicle with a lot more assurances included."