What Is an OBD-I Scanner?

check engine light
OBD-I scanners are simpler than OBD-II units, and you can often get by without one. Patrick Wilson / E+ / Getty Images

The Beginning of Onboard Diagnostics

Most vehicles that were manufactured prior to 1996 use first generation onboard diagnostic (OBD) systems that are collectively referred to as OBD-I. The first OBD-I systems showed up in the late 1970s and early 1980s, and every manufacturer developed their own interface technology.

That means that while these systems are grouped together into the general category of OBD-I, they share very little in common.

Every manufacturer had its own, proprietary OBD-I plugs and jacks, and many OBD-I scanners were designed to work with vehicles from only a single make or even model.

The good news is that, in many cases, you don't actually need an OBD-I scanner to read codes. The bad news is that every OEM had its own way of accessing codes without any diagnostic tools, so the situation is anything but simple.

OBD-I Scanners

Unlike OBD-II scanners, an OBD-I scanner that works with one make isn’t necessarily going to work with another. However, some of these scanners are designed to be universal, or at least work with multiple makes and models. OEM-specific OBD-I scanners have hard-wired connectors and software that is only capable of interfacing with the onboard computers of a single manufacturer.

Universal and multi-OEM scanners have interchangeable connectors and software that can handle more than one make of vehicle.

Some of these scanners also have interchangeable cartridges or modules that allow them to switch between different OEMs.

What Can an OBD-I Scanner Do?

OBD-I scanners lack many of the features and abilities of OBD-II scanners due to the limitations of OBD-I systems. Accordingly, the specific features of any scanner will depend as much on the particular OBD-I system that you’re dealing with as they will on the scanner itself.

OBD-I scanners typically provide basic access to data streams, and you may be able to access freeze-frame data, tables, and similar information.

The most basic OBD-I scanners are more like simple code readers, in that all they can do is display codes. In fact, these basic OBD-I scanners will actually “display” the codes with a blinking light that you have to count. Some OBD-I scanners can clear codes, and others require you to clear the codes with a basic procedure like disconnecting the battery or removing an ECM fuse.

Combination OBD-I / OBD-II Scan Tools

Some code readers and scan tools are capable of dealing with both OBD-I and OBD-II systems. These scanners include software that can deal with the pre-1996 onboard computers from multiple OEMs, software that can interface with post-1996 OBD-II systems, and multiple connectors to interface with all of the above. Professional technicians typically use combination scanners that can deal with just about anything, but there are also consumer-grade devices available that are good for DIYers who own both older and newer vehicles.

Reading Codes Without an OBD-I Scan Tool

Most OBD-I systems include built-in functionality that allows you to read codes by blinking the check engine light, but the process varies from one OEM to the next.

Chrysler is one of the easiest, as all you have to do is turn the ignition key on and off several times. The exact procedure is: on, off, on, off, on, and then leave it on, but don't start the engine. The check engine light will then blink to indicate which codes are stored. For instance, one blink, followed by a short pause, followed by seven more blinks would indicate a code 17.

Other makes, like Ford and General Motors, are a little more complicated. These vehicles require you to short out terminals in the diagnostic connector, which will cause the check engine light to blink out the codes. Before you attempt to read codes on one of these vehicles, it's a good idea to look up a diagram of the diagnostic connector on your car to make sure you get the right terminals.