Where's the port? On Isuzu trucks (NPR, NQR, F-series) it's in the cab — under the dash near the steering column, behind the driver's kick panel, or by the fuse box. On Volvo trucks (VNL) it's a round 9-pin Deutsch connector under the dash, lower-left of the column. The Isuzu D-Max pickup is different — a standard 16-pin car port. And whatever the port: a car OBD-II scanner can't talk J1939, so you need a heavy-duty-capable tool.
Truck OBD Port Locations (Start Here)
This is the question that strands most people first, so here's where to look before you worry about pinouts.
Isuzu Trucks (NPR, NQR, NRR, F-series, Forward, Giga)
On Isuzu medium- and heavy-duty trucks the diagnostic port is almost always in the cab. The usual spots are under the dash to the left or right of the steering column, behind the driver's-side kick panel near the door, or near the interior fuse box (sometimes behind a small cover). It looks like a car OBD-II socket but is wired for Isuzu's truck protocols.
Isuzu D-Max (This One's Different)
Note the D-Max is a light-duty pickup, not a medium-duty truck. It uses a standard 16-pin OBD-II port, 12V, under the dash near the steering column — and it works with normal car scan tools. Don't confuse it with the NPR/NQR truck range.
Volvo Trucks (VNL and Similar)
On most modern Volvo trucks the round 9-pin Deutsch connector sits under the dash, typically to the lower-left of the steering column. Some 2013-and-newer Volvos add a 16-pin OBD-II-style connector alongside the Deutsch — more on that below.
Why a Car Scanner Fails on a Truck
Standard automotive OBD-II is built mainly for emissions and basic powertrain diagnostics on light vehicles. Heavy trucks need far more — a network managing the engine, transmission, ABS, body controllers and more — so they run different standards.
Two dominate commercial trucks: SAE J1939, the modern high-speed standard running on CAN bus, and the older, slower SAE J1708/J1587. J1939 has largely replaced J1708, but you'll still find J1708 on some pre-2007 trucks, or running alongside J1939 on newer ones. Using a basic car OBD-II scanner on a J1939 system is like two people speaking different languages — they can't understand each other.
| Feature | Standard OBD-II (cars) | J1939 (heavy trucks) |
|---|---|---|
| Primary use | Emissions & engine | Full vehicle network |
| Connector | 16-pin J1962 (D-shaped) | 9-pin Deutsch (black/green) |
| Voltage | 12V | 12V or 24V |
| CAN speed | 500 kbps | 250 kbps (black) / 500 kbps (green) |
The Isuzu Truck OBD Pinout (16-Pin)
Isuzu medium-duty trucks set a trap: many NPR, NQR and F-series models use a 16-pin connector that looks identical to a car's OBD-II port, but it's wired for truck protocols. You need this layout to connect the right adapter or verify the port's integrity.
| Pin | Function |
|---|---|
| 4 | Chassis ground |
| 5 | Signal ground |
| 6 | CAN High (J-2284) |
| 7 | K-Line (ISO 9141-2) |
| 12 | Proprietary (often TCM or ABS) |
| 14 | CAN Low (J-2284) |
| 16 | Battery power (+) |
Other pins carry manufacturer-specific functions, so always check the specific model's service manual for the definitive layout. Connector integrity is a real-world culprit too — electrical faults cause a large share of unscheduled truck downtime, and a spread or corroded pin is invisible but will stop communication dead.
The Volvo Truck OBD Pinout (9-Pin Deutsch)
Volvo sticks closer to the North American heavy-duty standard, so most Volvo trucks use the round 9-pin Deutsch connector as the main diagnostic point. If you work on a Volvo fleet, this is the layout for scanners, telematics and loggers.
| Pin | Function | Description |
|---|---|---|
| A | Ground | Battery (−) / main ground |
| B | Battery power | Unswitched +12V or +24V |
| C | CAN_H | J1939 high side |
| D | CAN_L | J1939 low side |
| E | CAN Shield | Shield/ground against interference |
| F | J1708 (+) | Positive line, older protocol |
| G | J1708 (−) | Negative line, older protocol |
| H / J | Proprietary | OEM use / implement bus |
There is no "Pin I" on a Deutsch 9-pin. The pin letters run A–H and then jump to J, deliberately skipping "I" to avoid confusion with the number 1. If a diagram shows a "Pin I," it's wrong — double-check before you probe.
Black vs Green — What the Colour Means
Both black and green 9-pin connectors carry J1939. The difference is speed: the older black (Type 1) runs J1939 at 250 kbps plus J1708 on the older pins, while the newer green (Type 2), rolled out from around 2016, runs at 500 kbps. Green is physically keyed so older 250 kbps-only tools can't be forced onto a 500 kbps bus and cause damage — and green adapters are backward-compatible with black ports. The SAE J1939-13 connector spec defines the standard in detail.
What If My Volvo Has a 16-Pin Port?
Some Volvos, especially 2013-and-newer, add a 16-pin OBD-II-style connector alongside the Deutsch. On that connector Volvo routes J1939 high to pin 3 and J1939 low to pin 11 — so a heavy-duty tool can connect there too, but confirm which connector your scanner's cable is built for.
5-Minute Test: Is It the Port or the Tool?
Before you blame an expensive ECU or a new scan tool, spend five minutes with a multimeter to confirm the port has what it needs.
- Safety first. Wear safety glasses, set the ignition to the correct position for each test, and use sharp, good-quality probes so you don't short adjacent pins.
- Check for power. Set the multimeter to DC volts above 24V (e.g. 40V). Red probe on the power pin (Volvo Pin B; Isuzu Pin 16), black probe on a known-good ground. You want ~12V or ~24V. No reading means a blown fuse or power-feed fault.
- Check for ground. Switch to continuity/resistance. One probe on the ground pin (Volvo Pin A; Isuzu Pin 4), the other on a known-good chassis ground. It should read near zero ohms / beep. A high reading means a bad ground path.
- Check the CAN bus. With ignition fully OFF, set the meter to resistance and measure between the two CAN pins (Volvo Pin C/D; Isuzu Pin 6/14). A healthy bus reads around 60 Ω (two 120 Ω terminating resistors in parallel). A very different value points to a bus fault.
The ~60 Ω CAN reading is the key diagnostic: a healthy J1939 bus has two 120 Ω terminating resistors in parallel, so you should measure about 60 Ω across the CAN pins with the ignition OFF. A reading near 120 Ω means one terminator is missing; near-zero or open-circuit means a short or break in the bus wiring — either way, the fault is in the truck, not your tool.
Choosing a Scan Tool That Talks J1939
The whole point of the pinout is to get a tool talking to the truck — and that means a scanner built for heavy-duty protocols, not a car code reader. Look for native 9-pin Deutsch (J1939) support, both 250 and 500 kbps, J1708/J1587 fallback for older trucks, 24V tolerance, and ideally multi-brand truck coverage.
If you service trucks regularly, a dedicated tool like the D9HD Full Diagnostic Scanner for Trucks covers J1939 across these connectors and voltages, so you're not caught out by a black-vs-green speed mismatch or a 24V system. You can read the SAE J1939 standard overview for the protocol background.
Not sure which connector or cable your truck uses — black vs green 9-pin, Isuzu 16-pin, or a J1708 setup? Send us your make, model and year and we'll confirm the correct diagnostic connector or adapter cable for your vehicle. Get a matched connector — contact us →
Frequently Asked Questions
Where is the OBD port on an Isuzu truck (NPR, NQR, F-series)?
On Isuzu medium- and heavy-duty trucks the diagnostic port is almost always inside the cab. The usual spots are under the dash to the left or right of the steering column, behind the driver's-side kick panel near the door, or near the interior fuse box (sometimes behind a small cover). It looks like a car OBD-II socket but is wired for Isuzu's truck protocols.
Where is the diagnostic port on a Volvo truck (VNL)?
On most modern Volvo trucks the round 9-pin Deutsch connector sits under the dash, typically to the lower-left of the steering column. Some 2013-and-newer Volvos also add a 16-pin OBD-II-style connector alongside the Deutsch. Either way you need a heavy-duty-capable scan tool — a car OBD-II reader can't talk J1939.
Is the Isuzu D-Max OBD port the same as an Isuzu truck?
No — this trips people up. The D-Max is a light-duty pickup, not a medium-duty truck. It uses a standard 16-pin OBD-II port at 12V, under the dash near the steering column, and works with normal car scan tools. The NPR/NQR/F-series trucks are the ones that use truck protocols on a look-alike connector.
What does black vs green mean on a 9-pin Deutsch connector?
Both black and green 9-pin connectors carry J1939 — the difference is speed. The older black (Type 1) runs J1939 at 250 kbps; the newer green (Type 2), rolled out from around 2016, runs at 500 kbps. Green is physically keyed so an older 250 kbps-only tool can't be forced onto a 500 kbps bus, and green adapters are backward-compatible with black ports.
Why won't my car OBD-II scanner work on a truck?
Because trucks speak a different language. Standard car OBD-II is built for emissions and basic powertrain data on light vehicles, while heavy trucks run SAE J1939 (and older J1708/J1587) across a full vehicle network. A basic car scanner physically may plug in on some ports but can't communicate with a J1939 system — you need a scan tool with native heavy-duty protocol support.
How do I test if the OBD port itself is faulty?
Spend five minutes with a multimeter before blaming the ECU or tool. Check for power (red probe on the power pin — Volvo Pin B, Isuzu Pin 16 — expecting ~12V or ~24V), check for ground (continuity between the ground pin and chassis), and check the CAN bus (with ignition OFF, resistance across the two CAN pins should read around 60 Ω on a healthy bus). No power, no ground, or a wrong CAN reading points to a port or wiring fault.
