Since 1996, all cars and light trucks sold in the United States have been required to be OBD-II compliant. This standardization was mandated to help diagnose vehicle issues, but the system isn’t quite as simple as “one size fits all.” While all OBD-II vehicles use a standardized connector, they communicate using different protocols. Understanding what OBD2 protocol your car uses is crucial for effective diagnostics and using OBD-II tools correctly.
To understand which protocol your vehicle employs, it’s helpful to first know that OBD-II compliance in the European Union has a more complex history. However, regardless of location, OBD-II compliant vehicles utilize one of five main communication protocols: J1850 PWM, J1850 VPW, ISO9141-2, ISO14230-4 (Keyword Protocol 2000), and the more modern ISO15765-4/SAE J2480 (CAN). Notably, in the US, car manufacturers were restricted from using the CAN protocol until the 2003 model year, but since 2008, CAN has become the standard protocol for all vehicles.
Before diving into protocols, let’s quickly touch on the physical connector you’ll be using: the Diagnostic Link Connector (DLC). SAE J1962 defines two types: Type A and Type B. The primary difference lies in the alignment tab’s shape.
Locating the DLC
SAE J1962 dictates the location of the Type A DLC “shall be located in the passenger or driver’s compartment in the area bounded by the driver’s end of the instrument panel to 300 mm (~1 ft) beyond the vehicle centerline, attached to the instrument panel and easy to access from the driver’s seat. The preferred location is between the steering column and the vehicle centerline.” Essentially, look under your dashboard on the driver’s side.
Type B DLCs have a slightly broader location allowance, “shall be located in the passenger or driver’s compartment… and an imagined line 750 mm (~2.5 ft) beyond the vehicle centerline… easy to access from the driver’s seat or from the Co-drivers seat or from the outside.”
Fig. 1 – Type A J1962 DLC connector, commonly found under the dashboard on the driver’s side.
Fig. 2 – Type B J1962 DLC connector, another variation for accessing vehicle diagnostics.
Determining Your OBD2 Protocol Through Pinout
A practical method to identify your vehicle’s OBD2 protocol is by examining the pinout of the DLC. By looking at which pins are populated in your OBD-II connector, you can deduce the protocol in use.
Fig. 3 – OBDII J1962 connector pinout diagram illustrating pin assignments for different protocols.
The table below simplifies protocol identification based on pin presence:
| Pin 2 | Pin 6 | Pin 7 | Pin 10 | Pin 14 | Pin 15 | Standard |
|---|---|---|---|---|---|---|
| must have | – | – | must have | – | – | J1850 PWM |
| must have | – | – | – | – | – | J1850 VPW |
| – | – | must have | – | – | may have* | ISO9141/14230 |
| – | must have | – | – | must have | – | ISO15765 (CAN) |
*Pin 15 (L-line) is optional in newer vehicles using ISO9141-2 or ISO14230-4 protocols.
To further clarify, here’s a breakdown of the essential pins for each protocol:
PWM Requires pins 2, 4, 5, 10, and 16 VPW Requires pins 2, 4, 5, and 16, but not 10 ISO Requires pins 4, 5, 7, and 16. Pin 15 may be present CAN Requires pins 4, 5, 6, 14, and 16
Pins 4 (Chassis Ground), 5 (Signal Ground), and 16 (Battery Positive) are standard across all OBD-II compliant vehicles, in addition to the protocol-specific pins mentioned above.
Why Knowing Your Protocol Matters
Identifying what OBD2 protocol your car uses is essential for several reasons. It ensures compatibility with diagnostic tools and scanners, allowing you to accurately read trouble codes, monitor vehicle parameters, and perform necessary repairs. Using an incompatible tool can lead to communication errors or even damage to your vehicle’s electronic systems.
For a more comprehensive list of protocols by manufacturer, you may find resources like OBDII Generic Communication Protocols by Manufacturer helpful for general guidance. However, physically checking your DLC pinout remains the most reliable method to determine the OBD2 protocol your car utilizes.
