Cars Cats Computers — DIY car diagnostics with | carscatscomputers.com
Which cars carry the 16-pin port, where to find it, and why one adapter does not speak to every car.
Whether your car can talk to a laptop at all is a question of date and market. In the US, OBD-II is mandatory on every gasoline car and light truck from model year 1996, and California required the same hardware from 1994. In the EU, EOBD became compulsory on all new petrol cars from 1 January 2001 and on new diesels from 2004.
Inside those dates the hardware is standardised. The diagnostic connector is SAE J1962: 16 pins in two rows of eight inside a trapezoidal housing, mounted within easy reach of the driver — look under the dash, around the steering column or the centre console.
On narrow screens, swipe or scroll the plate sideways.
The pins are shared between several possible buses. Pins 6 and 14 carry CAN high and CAN low, the pairing used by the fastest protocol. Other pins serve the older standards, which is why the same shell shape fits cars built decades apart.
Four protocol families turn up under the shell, at three different speeds. CAN runs at 500 kbit/s; SAE J1850 PWM at 41.6 kbit/s; SAE J1850 VPW at 10.4 kbit/s; and ISO 9141-2 with KWP2000 at 10.4 kbaud. An adapter that speaks only CAN will read most newer cars and say nothing at all on an older import — that mismatch, not a dead car, is the usual reason a scanner stays silent.
Once the link is up, everything else is one standard: SAE J1979 defines the services that read trouble codes, the freeze frame (service 02) and live-data PIDs such as engine speed and coolant temperature. The code format those services return is decoded on the companion page How to Read a Trouble Code: P0301 and Friends.
Further reading