OBD-II Connector Pinout & Port Tester

Connector Layout (J1962 16-pin)

The OBD-II port is a trapezoidal 16-pin connector. Viewed looking at the face of the female port (as mounted in the car), pins are numbered 1-8 across the top row and 9-16 across the bottom row, left to right:

Pin 16 is always in the bottom-right corner when looking at the port from the driver's footwell.

Pin Function Reference

Not every pin is populated on every vehicle -- manufacturers only wire the pins their protocol uses. Pins 4, 5, and 16 are always present (ground and power). The others vary by protocol.

The Five OBD-II Protocols

OBD-II uses five physical protocols. Since 2008, CAN (ISO 15765-4) has been mandatory in the U.S. -- but older vehicles use one of the four legacy protocols, and your scanner needs to support it.

Which Protocol Does My Vehicle Use?

Where Is the OBD-II Port?

Looking for the port on a specific car? This page covers what the standard requires and what each pin does. For the location on your exact make and model, use the OBD2 port location by car guide — it lists where the connector actually sits on each manufacturer.

SAE J1962 requires the DLC to be in the passenger compartment, attached to the instrument panel in the area from the driver's end of the panel to 300 mm (about a foot) beyond the vehicle centerline, accessible from the driver's seat — and reachable without any tool to remove a cover or barrier. The standard's preferred spot is between the steering column and the vehicle centerline, which is why it's almost always right under the dash by your left knee. Sometimes it isn't.

Two more things the standard says that explain why the port can be hard to find. It must be out of the occupants' normal line of sight but easily visible to a technician crouched at the door — so manufacturers are actively required to tuck it away. And US OBD regulations are more restrictive than J1962 itself, which is why the light-duty port location is more consistent in practice than the standard alone would guarantee.

Type A vs Type B: why some trucks look different

J1962 defines two connector types, and this is the part most pinout charts leave out. Type A is the familiar 12-volt light-duty connector on every car and light truck — the one this page's pin table describes. Type B is the 24-volt variant used on many medium- and heavy-duty vehicles.

• Look for blue. The standard requires the front of the D-shaped area on a Type B connector to be marked in blue — that colour is the 24-volt warning, and it is the fastest way to tell the two apart before you plug anything in.
• Mating is deliberately one-way. A Type B scan-tool plug is specified to mate with both Type A and Type B vehicle connectors; a Type A tool plug mates only with a Type A vehicle connector. So a 12-volt-only tool physically cannot be connected to a 24-volt Type B vehicle.
• Pin 16 carries 24 V DC on Type B (minimum 2.0 A supply), against 12 V on Type A — same contact number, different supply.
• Type B gets a wider location allowance — out to 750 mm beyond the vehicle centerline (versus 300 mm for Type A), and it may be reachable from the co-driver's seat or from outside the cab rather than only from the driver's seat. That is why the port on a commercial truck can turn up somewhere a car owner would never look.
• Both are 16-contact connectors — the difference is supply voltage, marking, and mating compatibility, not the number of pins.

If you are working on a commercial truck, the diagnostic connector may not be J1962 at all — heavy trucks commonly use the 9-pin Deutsch (J1939) connector instead. See the heavy-duty diesel section.

Common locations

• Under the dash, driver's side, near the steering column. The default location on most vehicles.
• Under the dash, center or passenger side. Common on some Chrysler, Honda, and older Ford models.
• Behind an ashtray or coin tray. Typical on some BMWs and Mercedes models.

Unusual locations by make

Can't find the port? The Equipment and Tool Institute maintains a free DLC location database, and the under-dash EPA emissions sticker on 1996+ U.S.-market vehicles usually mentions it.

Troubleshooting a Dead OBD Port

• No power to scanner. Check battery voltage at pin 16 -- should read ~12V with key off. If 0V, check the OBD-II fuse (often labeled "Cigar," "Data Link," or "DLC") in the dash fuse box.
• Scanner powers on but won't connect. Verify you're on the right protocol. Low-cost OBD tools sometimes only speak CAN -- won't work on pre-2008 vehicles with PWM/VPW/ISO.
• Intermittent connection. Check the scanner cable and the port terminals for pushed-back or corroded pins. Port sits near the driver's feet and gets kicked.
• Scanner works sometimes but drops. Low battery voltage causes loss of CAN bus sync. Put a maintainer on the battery before long diagnostic sessions.
• Chassis ground (pin 4) bad. Usually shows as garbled data or scanner reboot. Test continuity from pin 4 to a known chassis point.

Interactive Port Tester

Tap each pin to record whether a terminal is fitted, enter what your meter reads, and this works out which protocol the vehicle uses and what is wrong if the port is dead. Nothing is uploaded — your readings stay in this browser and survive a page reload, so you can climb out from under the dash without losing them.

Related Quick References