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Its original name is an ALDL, short for Assembly Line Diagnostic Link, or Assembly Line Data Link. But most call an ALDL the OBD-II port because it provides everyone from engineers at proving grounds to dealership technicians to shade tree mechanics a connection to the vehicle’s software and diagnostic systems. And soon, battery electric as well as hydrogen fuel cell vehicles will offer similar access.

Wait… EVs don’t already have that? Not all of them, no. And the various manufacturers’ systems differ from each other in both connectivity and scope, which makes troubleshooting an errant EV that much more difficult. That, as you can imagine, causes more than a few headaches for the good folks who service EVs.

Modern onboard diagnostics, or OBD-II, became a standardized and mandatory part of every automobile sold in the United States, starting with the 1996 model year. All vehicles, from a Ford Escape to a Ferrari SF90, needed one. But this mandate exempted EVs and other alternatively powered vehicles.


Well, the history that led to OBD-II will help explain that. The ALDL port originated from General Motors in the early 1980s in its pursuit to produce systems and diagnostics for its cars to meet new government emissions regulations. By the late ’80s, the California Air Resources Board (CARB) got involved and mandated that all 1991 model-year or newer cars sold there must include an onboard diagnostics system to manage and control emissions. The standardized system was an adaptation of GM’s ALDL.

But that system quickly proved inadequate, and CARB required a new, more complete controls check system, tagged OBD-II, for 1996 model year and newer cars, with diesels following suit in 1997. The federal government agreed with that requirement, and the modern OBD-II system became the law of the land. Its core purpose was to ensure cars meet tailpipe emissions standards, but since BEVs don’t have tailpipes, they were exempt.

As time passed, the ever-increasing number of emissions checks built into ever-increasingly powerful computer systems on vehicles would throw an ever-increasing amount of error codes. To simplify all of that, the vast majority of those error codes switched on the engine check or “idiot” light on the instrument cluster.

That led to onboard diagnostics systems or “code readers” quickly becoming essential for every vehicle technician to decipher what was running afoul of contemporary vehicles’ powertrains. More time passed, and virtually every problem on a vehicle would trigger some kind of sensor, which would then turn on some kind of error code, and the ubiquity of onboard diagnostics reached its zenith.

The ALDL port became so instrumental that it’s how I connected my laptop to prototype vehicles when I worked as a Slip Controls Engineer for TRW from 2007–2011. Through that port, I directly accessed the brake controls computer to upload new traction and stability control software directly into the car.

EVs don’t have tailpipe emissions

But as EVs become more mainstream, they include a variety of sensors and systems to keep everything running optimally, oftentimes more than any internal combustion engine-powered vehicles. As EVs accrue miles and experience wear, problems can and will occur. Currently, there is no set standard for accessing and diagnosing them.

That changes for 2026-and-newer model-year cars, courtesy of CARB once again, this time as part of its Advanced Clean Cars II protocol for cars sold in the state between 2026–2035. Part of California’s sweeping set of rules for cars sold in the state requires EVs, hydrogen fuel cells, and Plug-in Hybrids to follow a similar diagnostics standard, much like OBD-II did 30 years earlier.

As several states already follow California’s lead regarding vehicle standards, this will likely spread across the US and reach similar levels of ubiquity. Hopefully, the federal government will have it set by the time 2026 model-year cars start rolling down assembly lines.

The automotive industry is in the middle of a huge transition. As more internal combustion engines phase out, making room for the latest BEVs to take their place, all kinds of different elements of the industry will see some kind of disruption. This is one of them.

And there’s more than a bit of irony that a standard diagnostic system that began life to control tailpipe emissions is needed on vehicles with no tailpipe emissions.

The good news is—unlike building a dependable and standardized nationwide charging network—mandating a standard diagnostics system seems relatively achievable, at least for the established automakers out there. That’s how Honda sees it, anyway.

“American Honda, along with others in the industry, worked with the California Air Resources Board (CARB) as they created the upcoming EV diagnostic standardization requirements,” Chris Martin, a Honda spokesperson, said, “and we fully support the effort to develop a single framework. We are currently working to ensure that our future EV models will meet the CARB ACC2 requirements.”

For startups, on the other hand, this may prove to be yet another thing to have to learn. It turns out building cars isn’t easy. But soon, diagnosing problems and keeping cars on the road will get a little easier.

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