On Board Diagnostics (OBD)-II is a standardized diagnostic interface required on new vehicles sold in the United States on or after 1 January 1996. The vehicle’s on board computer must feature an OBD-II connector that allows a professional mechanic or a do-it-yourself (DIY) mechanic to connect diagnostic software that can analyze problems and check the health of the vehicle. There are three different pin-out configurations possible in the OBD-II connector that are all compliant with OBD-II standards.

Knowing the type of OBD-II your vehicle has is handy if you are a DIY mechanic who plans to get automotive diagnostics software. Not all software packages are compliant with all three types of OBD-II, and though universal software is available, it is more expensive.

All OBD-II interfaces are 16-pin, female connectors that roughly resemble a computer’s parallel connector in size and shape. The connector has metallic contacts in most of the pin-out holes, with two rows of eight pin-outs each. By making a close inspection of the pin-out configuration you should be able to verify the OBD-II protocol. The three different communication protocols for OBD-II connectors are:

SAE J1850 VPW (Variable Pulse Modulation): Used in most General Motors vehicles and light trucks. Look for metallic contacts populating pins #2, #4, #5 and #16. Pin-out #10 should be empty.

SAE J1850 PWM (Pulse Width Modulation): Used in Ford vehicles. Check for metallic contacts in pin #2, #4, #5, #10 and #16.

ISO 9141-2: Used in Chrysler vehicles and most imports. Populated pins should include #4, #5, #7, #15 and #16.

Variations do exist among certain models that are manufactured and branded as American, but are actually derivatives of German or Asian imports, for example. In this case the vehicle might follow the ISO 9141-2 OBD-II standard.

If your car has an OBD-style connector but the pins are populated differently, it was probably manufactured prior to late 1995. Also, if the vehicle is pre-OBD-II, the connector might still match one of the configurations described previously without being OBD-II compliant. Vehicles that are OBD-II compliant normally have a sticker on the underside of the hood identifying the vehicle as such.