OBD-II vs 9-Pin vs 6-Pin: Which ELD Port Does Your Truck Have?

The three ports at a glance

Model years are rough guides. Truck makers changed connectors at different times, and some trucks carry more than one port. The connector you can see and count is the one that matters.

OBD-II: light duty and many medium duty

OBD-II is the same port a shop plugs into on a passenger car. It is a 16-pin trapezoid, wider at the top than the bottom. Most cars and light trucks built for the U.S. since 1996 have one. EPA extended on-board diagnostics to heavier vehicles up to 14,000 lbs GVWR in the 2000s, so many newer medium-duty trucks have one too.

If you run a sprinter van, a cargo van, a hotshot pickup, or a non-CDL box truck, you almost certainly have an OBD-II port. Whether you need an ELD in that vehicle at all depends on weight and how you operate. See ELD under 10,000 lbs, sprinter and cargo van ELD, and box truck ELD.

9-pin J1939: most heavy trucks

The 9-pin round Deutsch connector carries the J1939 data network that heavy-duty engines use. If your Class 8 tractor was built after about 2001, this is the most likely port. It has a locking collar you twist to seat.

Look at the color. Older 9-pin connectors are usually black. Newer ones are often green, which signals a higher data speed. Otherwise the two look alike, so mention the color if you call about compatibility.

6-pin J1708: older heavy trucks

The 6-pin round connector carries the older J1708 data link. You see it on heavy trucks from before the J1939 changeover, roughly the 1990s into the early 2000s. It looks like a smaller version of the 9-pin, with the same twist-lock collar.

One thing to check if your truck is that old: vehicles manufactured before model year 2000 can use paper logs instead of an ELD under 49 CFR 395.8(a)(1)(ii). The rule looks at the vehicle identification number on the registration. Details in ELD exemptions.

Volvo, Mack, and Peterbilt: when you need an adapter

Some heavy trucks do not use the round connector at all. Many Volvo and Mack trucks from about the 2014 model year on have a 16-pin port that looks like OBD-II but carries heavy-duty engine data. A standard OBD-II plug-in will not read it correctly, so the ELD needs a cable made for that truck. Some Peterbilt models also need a specific adapter.

The PT-40 has adapter cables available for Volvo, Mack, and Peterbilt. When you order, give us the make, model, and year so you get the right connection the first time.

How to identify your port in a minute

1. Look under the dash on the driver side. On light-duty vehicles, check above the pedals and near the steering column. On heavy trucks, look low, near the driver's knee or the parking brake valve.
2. Check the shape. A flat trapezoid is a 16-pin port. A round connector with a twist collar is a heavy-duty Deutsch port.
3. Count the pins. Round with 9 pins is J1939. Round with 6 pins is J1708.
4. Note the make and year. If it is a 16-pin port on a Volvo, Mack, or Peterbilt heavy truck, plan on an adapter cable.
5. Still not sure? Take a photo of the port and call (720) 362-3783 before you order.

Before you plug anything in

• Never force a connector. If it does not slide in, it is the wrong plug or the wrong orientation.
• Look for bent, corroded, or pushed-back pins. A damaged port causes dropouts that look like an ELD problem.
• Route the cable away from the pedals and the steering column, and zip-tie it so it cannot be kicked loose.
• If a shop scan tool also uses the port, unplug the ELD for the service visit and reconnect it after.

Once you know your port, the PT-40 installation guide covers plugging in and checking the connection. Order at /buy/.