OBD2 Pin Configurations and Protocols

The female 16-pin (2x8) J1962 connection is specified in the OBD2 specification as a standard, unified hardware interface. Under the OBD2 interface, there are five protocols in use, and it's generally able to estimate which one is in use based on the pins that are present on the J1962 connector

Understanding OBD2 Pin Configuration

Below is a comprehensive layout of the OBD2 pin configuration:

·       The pin configuration of the OBD2 16-pin diagnostic connection is often termed as a J1962 connector.

·       Pin 16 is linked to the vehicle's battery and provides electricity.

·       P ins 4 and 5 are used for grounding.

·       CAN Bus High and CAN Bus Low signals are coupled with pins 6 and 14, respectively.

·       The SAE J1850 protocol is used on pins 2 and 10, with pin 2 representing positive and pin 10 representing negative.

·       The ISO9141 protocol K-line and L-line are used on pins 7 and 15, respectively.

·       Pins 1, 3, 8, 9, 11, 12, and 13 are left unused and can be wisely exploited by an automobile manufacturer for performing other functions.  

An OBD2 Compliant Vehicle can Use Any of the Five Communication Protocols

ISO 15765: ISO 15765 is a global standard for data transmission over CAN bus. CAN comprises two main wires - CAN High and CAN Low wires. During data transmission, the CAN High voltage hits 3.75V. The CAN Low voltage lowers to 1.25V simultaneously. Both CAN High and CAN Low stay at 2.5V while the CAN bus is not transferring any data. ISO 15765 standard specifies a maximum data rate of 1Mbps. Pin 6 corresponds to CAN High, whereas pin 14 is connected to CAN Low.

ISO 9141-2: ISO 9141-2 employs two signals, K and L, for asynchronous serial communication. The K signal is used for the majority of OBD2 connections. The L signal is used to begin the bus's start-up. The highest data rate is 10.4 kilobytes per second (kbps), and the maximum signal voltage is 12 volts. The K-Line is connected to pin 7 of the OBD2 port, whereas the L-Line is connected to pin 15.

ISO14230-4 (KWP2000)

ISO9141 K-Line is a very common protocol for automobiles built after 2003. Pin 7 is used for accessing this protocol. 

ISO14230-4 is available in two versions:

·       ISO 14230-4 KWP (5 baud init)

·       ISO 14230-4 KWP (fast init)

These versions of the protocol differ slightly in the methods used for establishment of communication. Both the variants employ a bit rate of 10400 bits per second.

SAE J1850 (PWM): The Society of Automotive Engineers developed the SAE J1850 protocol (SAE). The Pulse Width Modulation technique is used to implement SAE J1850 PWM utilising a differential transmission mechanism. PWM has a signal rate of 41.6 kbps. The maximum voltage is 5 volts. Pins 2 and 10 of the OBD2 port are coupled to SAE J1850 Bus (positive) and SAE J1850 Bus (negative) respectively.

SAE J1850 (VPW): The Variable Pulse Width approach is used to implement SAE J1850 VPW, which requires one signal wire and one ground wire. PWM has a signal rate of 10.4 kbps. The highest permissible voltage is 7 volts.