Extending the OBD2 connector, wiring it yourself, understanding the pin assignment
The 16-pin OBD2 socket is the standard interface for vehicle diagnostics. In everyday workshop life, however, a direct connection is not always enough: the socket is located deep in the footwell, a test setup needs its own OBD2 connection, or a self-made lead is damaged. This article explains the pin assignment of the OBD2 socket and shows which accessories help in which situation.
The pin assignment of the OBD2 socket
The assignment of the 16 contacts is standardised (SAE J1962 / ISO 15031-3). Some pins are fixed, while others may be assigned by the manufacturers themselves:
| Pin | Assignment |
|---|---|
| 1 | Manufacturer-specific |
| 2 | SAE J1850 bus + (PWM/VPW) |
| 3 | Manufacturer-specific |
| 4 | Chassis ground (body) |
| 5 | Signal ground |
| 6 | CAN High (ISO 15765-4) |
| 7 | K-line (ISO 9141-2 / ISO 14230-4) |
| 8 | Manufacturer-specific |
| 9 | Manufacturer-specific |
| 10 | SAE J1850 bus − (PWM) |
| 11 | Manufacturer-specific |
| 12 | Manufacturer-specific |
| 13 | Manufacturer-specific |
| 14 | CAN Low (ISO 15765-4) |
| 15 | L-line (ISO 9141-2 / ISO 14230-4) |
| 16 | Battery positive (permanent positive) |
Which lines a vehicle actually uses depends on the communication protocol: modern vehicles mainly communicate via CAN (pins 6 and 14), older European vehicles often via the K-line (pin 7). When checking the socket, you typically measure pin 16 against pin 4 or 5 first – battery voltage should be present there.
You can read more about the socket, its location and the legal requirement in our article OBD connector: all questions and answers.
Three accessories – three use cases
| Situation | The right part |
|---|---|
| The socket is awkwardly placed and the tool should rest on the seat or workshop trolley | OBD2 extension cable 2 metres |
| Your own test setup or special wiring with an OBD2 connection | OBD2 cable with open wire ends |
| Building your own lead or replacing a damaged connector | OBD2 connector housing 16-pin |
OBD2 extension cable – 2 metres more freedom of movement
In many vehicles the diagnostic connector is located deep in the footwell. With the extension (16-pin OBD2 plug to 16-pin OBD2 socket) you can conveniently place the diagnostic tool on the seat or workshop trolley without pulling on the cable. This protects the plug and socket and makes long diagnostic sessions more comfortable.
OBD2 cable with open wire ends – for your own wiring
On one side a standardised 16-pin OBD2 plug, on the other free cable ends: this lets you integrate an OBD2 connection into test benches, ECU test setups or your workshop's own solutions. You determine the assignment of the open ends yourself – based on the pin assignment above.
OBD2 connector housing – for assembling your own leads
The housing or plug part in the standardised 16-pin format – without cable. Ideal for building your own diagnostic leads and adapters or for replacing a damaged connector housing on an existing lead.
Safety note
Connecting open wire ends and assembling connectors requires specialist knowledge. Check and document the pin assignment before assembly. Pin 16 carries permanent positive – a short circuit to ground can blow fuses or damage components. Work on vehicle electrics belongs in expert hands.
Important: An adapter cable is not a diagnostic tool. It only provides the mechanical and electrical connection between the vehicle and the diagnostic tool. Which control units and functions you can reach always depends on the diagnostic tool used, its software and the manufacturer, model and model year of the vehicle.
Conclusion
With the pin assignment in mind and the right accessories, the OBD2 socket becomes flexible: an extension for more freedom of movement, a cable with open wire ends for your own setups, a connector housing for DIY builds and repairs. You will find adapters for older vehicles without an OBD2 socket in our guide OBD1 to OBD2 adapter cables. You can buy on invoice via Klarna or PayPal. Questions? 0711-3654 4645.