The OBD2 connector: where it is and what each pin carries
Every car with OBD2 has the same 16 pin female socket, shaped like a trapezium. What changes is where each make hides it and which pins it uses.
Where it is
The standard says it has to be inside the cabin, within reach of the driver’s seat and accessible without tools. On most cars it’s under the steering wheel, to the left of the steering column or above the pedals. Other common places:
- Behind a small cover in the dashboard, under the steering wheel or next to the fuse box.
- In the centre console, in front of the gear lever or under a storage tray.
- Behind a cover marked with the OBD symbol or letters.
If you can’t find it, look for a black rectangle about four centimetres wide with two rows of pins.
The 16 pins
| Pin | What it’s for |
|---|---|
| 1 | Manufacturer’s choice |
| 2 | J1850 bus, positive (US Ford and General Motors) |
| 3 | Manufacturer’s choice |
| 4 | Chassis ground |
| 5 | Signal ground |
| 6 | CAN high (ISO 15765-4) |
| 7 | K-line (ISO 9141-2 and ISO 14230-4) |
| 8 | Manufacturer’s choice |
| 9 | Manufacturer’s choice |
| 10 | J1850 bus, negative (Ford PWM only) |
| 11, 12 and 13 | Manufacturer’s choice |
| 14 | CAN low (ISO 15765-4) |
| 15 | L-line (ISO 9141-2 and ISO 14230-4, rarely used) |
| 16 | Battery positive, 12 volts at all times, even with the ignition off |
Each make uses the free pins for its own purposes: other CAN networks, a second K-line for the ABS or airbag on older cars, or nothing at all. That’s why an OBD2 adapter reads the standard data through pins 6 and 14 or pin 7, and the make-specific data depends on what’s on the others.
Why the adapter lights up with the ignition off
Pin 16 always carries battery voltage. That’s why the adapter lights up as soon as you plug it in and why, if it’s left in for several days, it can slowly drain the battery. If no light comes on when you plug it in, the first thing to check is the diagnostic socket fuse, which on many cars is the same one as the cigarette lighter.
Type A and type B
The socket on cars is type A, for 12 volts. Trucks and buses running on 24 volts use type B, which has a split centre key so a 12 volt device can’t be plugged in by mistake.
Next up: which adapter to plug in and which language your car speaks over those pins.
More guides
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The Spanish ITV and the OBD socket: what they read
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The OBD2 readiness monitors
What each monitor checks, why they show not ready and how they complete.
What OBD2 is and since when your car has it
What it’s for, the difference between OBD2 and EOBD, and the year it became mandatory.
The OBD2 connector: where it is and what each pin carries
Where to look for it and what each of its 16 pins is for.
The OBD2 protocols: how your car talks
CAN, K-line (ISO 9141-2 and KWP2000) and J1850: which car uses which.
The OBD2 modes, one by one
Live data, fault codes, clearing, pending, VIN and permanent: what each mode asks for.
OBD2 live data and its normal values
Rpm, temperatures, fuel trims, oxygen sensors, load and boost: what each PID is and which value is normal.
Coming soon
Mid to late October 2026
If you want to try it in your car before anyone else, send us your email and we will add you as a tester.
info@finalobd.com