Pin 6 is CAN High, pin 14 is CAN Low, pin 16 is permanent 12V, pin 4 is chassis ground and pin 5 is signal ground on every car sold in the UK.
OBD2 pinout — all 16 pins
Pin 1: manufacturer discretionary, often a second CAN or LIN line. Pin 2 (brown): SAE J1850 Bus+, used on Ford PWM and GM VPW vehicles, mostly pre-2008. Pin 3: manufacturer discretionary, Ford medium-speed CAN+ on many models. Pin 4 (black): chassis ground, should read under 0.1 ohm to a bare body earth point. Pin 5 (green): signal ground, the reference the scan tool measures against — a bad pin 5 kills communication.
Pin 6 (orange): CAN High (CAN_H) to ISO 15765-4, idling around 2.5 V and rising to about 3.5 V when a module transmits. Pin 7 (light blue): ISO 9141-2 / KWP2000 K-Line on older European and Asian vehicles. Pin 8: manufacturer discretionary, sometimes a wake-up or ignition-sense line. Pin 9: manufacturer discretionary, Ford medium-speed CAN− on many models. Pin 10 (purple): SAE J1850 Bus−, Ford PWM only.
Pins 11, 12 and 13 are manufacturer discretionary and rarely populated. Pin 14 (dark blue): CAN Low (CAN_L) to ISO 15765-4, idling around 2.5 V and dropping to about 1.5 V dominant. Pin 15 (light blue): ISO 9141-2 L-Line, an optional second K-Line wire. Pin 16 (red): battery positive, a permanent live that should read full battery voltage with the ignition off.
The OBD-II socket has been mandatory on every petrol car sold in the UK since 2001 and every diesel since 2004, as a 16-pin Type A connector within reach of the driver's seat. Pins 4, 5, 6, 14 and 16 are fixed by standard on every vehicle — the rest are left to the manufacturer, which is why a generic dongle always reads emissions data but only marque-specific software reads the deeper modules.
The five pins that matter on every car
Pin 16 is battery positive, fed through a fuse that is very often shared with the cigar lighter — if a scanner shows no power at all, that fuse is the first thing to check. Pin 4 is chassis ground, bonded straight to the body; anything over 0.1 ohm to a bare earth point means corrosion at the earth strap.
Pin 5 is signal ground, and a pushed-back pin 5 gives the classic 'scanner powers up but won't link' fault. Pin 6 (CAN High) and pin 14 (CAN Low) carry the diagnostic data on every car sold in the UK since 2008, both idling near 2.5 V and swinging apart when the bus is active.
How to test a dead OBD2 port with a multimeter
Set the meter to DC volts and measure pin 16 to pin 4 — you should see battery voltage, typically 12.4 to 12.7 V with the engine off. Repeat from pin 16 to pin 5 for the same reading. If either is missing, chase the diagnostic or cigar-lighter fuse and the earth point before touching anything else.
With the ignition OFF, switch the meter to resistance and measure between pin 6 and pin 14. A healthy CAN bus reads 60 ohms — the two 120 ohm terminating resistors in parallel. Around 120 ohms means one terminator or one branch of the bus is open. Near 0 ohms means CAN_H and CAN_L are shorted together. Infinite resistance means broken bus wiring or lost pins in the connector.
Wire colours quoted here are the common convention and are a guide only — always confirm against the vehicle's own wiring diagram before probing, and never back-probe with a sharp pin that will pierce the insulation.
Frequently asked questions
Which OBD2 pins are CAN High and CAN Low?
Pin 6 is CAN High (CAN_H) and pin 14 is CAN Low (CAN_L) on the standard 16-pin OBD-II connector, as defined by ISO 15765-4. Every car sold in the UK from 2008 onwards uses these two pins for diagnostics.
Which OBD2 pin is 12V power?
Pin 16 is battery positive and should read full battery voltage (12.4–12.7 V engine off) at all times, even with the ignition switched off. Pin 4 is chassis ground and pin 5 is signal ground.
How do I test an OBD2 port with a multimeter?
Set the meter to DC volts and measure pin 16 to pin 4 — you should see battery voltage. Then measure pin 16 to pin 5 for the same reading. Finally, with the ignition OFF, switch to resistance and measure pin 6 to pin 14: a healthy CAN bus reads 60 ohms, which is the two 120 ohm terminating resistors in parallel.
What does 60 ohms between pin 6 and pin 14 mean?
60 ohms is correct and means both CAN terminating resistors are intact. Around 120 ohms means one terminator or one branch of the bus is open. Near 0 ohms means CAN_H and CAN_L are shorted together. Infinite resistance means the bus wiring is broken or the connector has lost its pins.
Why won't my scanner connect to the OBD2 port?
The usual causes are a blown cigar-lighter or diagnostic fuse killing pin 16, a corroded or pushed-back ground pin, a shorted CAN line, or a module dragging the bus down. Check power and ground first, then 60 ohms across pins 6 and 14, before assuming the scan tool is at fault.
Is the OBD2 pinout the same on every car?
The connector shape and the core pins are standardised — 4, 5, 6, 14 and 16 are the same on every vehicle. Pins 1, 3, 8, 9, 11, 12 and 13 are manufacturer discretionary, so their function varies by marque and model year.