All You Need to Know About OBD2: A Comprehensive Guide (2023)

What is OBD2?

In short, OBD2, or On-Board Diagnostics Second Generation, is a vehicle diagnosis system found in modern cars and trucks.

It operates by monitoring the performance of various vehicle components and systems and reporting any concerns via a standardized diagnostics interface.

The OBD2 system collects data from sensors and other monitoring devices, which are then examined by the vehicle's engine control unit (ECU) to determine whether any issues need to be addressed. Problems with the engine, gearbox, emissions system, and others, are among the most common faults that OBD2 can discover.

These problems are your car's ways of telling you, that there is a problem by showing you the malfunction indicator light on your dashboard.

How does OBD2 work?

The OBD2 collects data from many sensors and monitoring devices installed in your car's engine and other systems.

If any problems are discovered, the OBD2 computer system analyzes the data and generates diagnostic trouble codes (DTC). These codes may be read with a diagnostic tool or device, which can assist you in identifying and correcting any problems with the vehicle's performance.

It works by connecting the tool to the OBD2 port, which is normally positioned beneath the car's dashboard (image shown below).

The OBD2 port has a standard pinout, or wiring schematic, which allows the diagnostic tool to connect with the onboard computer of the vehicle and collect DTCs.

The OBD2 pinout defines how each pin on the OBD2 port works. There are 16 pins in total, each with its unique function. E.g., pins 4 and 5 are used for ground connections, and pins 2 and 10 are used to interface with the car's internal computer (SAE J1850 BUS+). Pins 6 and 14, the most important in our opinion, are used to connect to the CAN Bus (ISO 15765-4).

How to use an OBD2 scanner?

Using an OBD2 scanner is a straightforward process that involves a few simple steps, i.e., you have an OBD2 scanner. The AutoPi TMU device can also be used as an OBD2 scanner.

Here's a basic overview of how to use an OBD2 scanner.

1. Locate the OBD2 port: The OBD2 port is often found under the dashboard on the driver's side of the vehicle. The most common places are seen in the image below.

2. Turn on the ignition: Turn the key to the "On" position, but do not start the engine. This will enable the OBD2 system to connect with the scanner.

3. Connect the scanner: Connect the OBD2 scanner to the port. Depending on the make and model of the vehicle, you might need additional cables or adapters.

4. Read the Diagnostic Trouble Codes (DTCs): Once the scanner is connected, follow the instructions by the manufacturer to read the DTCs from the car's onboard computer. The scanner may also display other relevant information, such as sensor reading and real-time data.

5. Interpret the results: After reviewing the DTCs, use the scanner's manual or internet resources to interpret the data. With each code, the scanner should offer a summary of the problem. Remember, that some codes may need additional testing or examination to determine the main cause of the problem.

6. Clear the codes: After identifying the issue, use the scanner to clear the DTCs. This will reset the system and turn off the dashboard's check engine light. Remember, that just clearing the codes without addressing the underlying problem may result in the check engine light returning.

Overall, using an OBD2 scanner may assist car owners and mechanics in diagnosing and addressing any performance issues with a vehicle. Car owners may save money on repairs and ensure their vehicle is functioning at peak performance by routinely checking the diagnostics using an OBD2 scanner.

OBD2 and CAN bus connection

The onboard diagnostics is a “higher layer protocol” and CAN is a method of communication. The OBD2 standard specifically specifies an OBD2 connector that contains a set of five viable protocols. In addition, the CAN bus has been a mandatory OBD2 protocol for all vehicles sold in the United States since 1996. From 2004 and later, all cars in Europe were required to be OBD2 compatible, and from 2006 and later in Australia and New Zealand.

The five OBD2 signal protocols

As mentioned above, the CAN bus serves as the basis for OBD2 communication in most cars today. When it comes to the OBD2 interface, there are 5 signaling protocols, and vehicles usually implement only one.

SAE J1850 (PWM) | 41.6 kB/s - Standard used in Ford Motor Company.

• Pin 2: Bus +

• Pin 10: Bus -

• High Voltage is +5 V

• 12 bytes message length, including CRC

• Employs a multi-master arbitration scheme called Carrier Sense Multiple Access with Non-Destructive Arbitration.

SAE J1850 (VPW) | 10.4/31.6 kB/s - Standard used in General Motors.

• Pin 2: Bus +

• Bus idles low

• High voltage is +7 V

• The decision point is +3.5 V

• 12 bytes message length, including CRC

• Employs CSMA/NDA

ISO 9141-2 | The protocol has an asynchronous serial data rate of 10.4 kbps. It is a bit similar to RS-232, but the signal levels vary. Usually used in Chrysler, European and Asian vehicles.

• Pin 7: K-line

• Pin 15: L-line is optional

• UART signaling

• K-line idles high - 510-ohm resistor to Vbatt

• The dominant state is driven low with an open collector driver

• Max 260 bytes message length. Max 255 data field.

ISO 14230 (KWP2000).

• Pin 7: K-line

• Pin 15: L-line is optional

• Physical layer identical to ISO 9141-2

• Data rate of 1.2 to 10.4 kBaud

• Up to 255 bytes of message length in the data field

ISO 15765 | 250 kbit/s or 500 kbit/s. The CAN bus protocol was developed by Bosch and is mandatory in many cars.

• Pin 6: CAN High

• Pin 14: CAN Low

• All OBD2 pinouts use the same connector. However, different pinouts are used for different purposes, except for pins 4 and 16.

The OBD2 connector and pinout

The OBD2 connector lets you access data from your car easily. This image of a connector pinout is an example of a female OBD2 16-pin (2x8) J1962 connector, which is a standardized hardware interface. In contrast to the OBD1 connector, which is usually found under the food of the vehicle, the OBD2 connector is in most cases required to be within 2 feet (0.61m) of the steering wheel. Here’s a detailed picture of the OBD2 Connector pinout.

History and the difference between OBD1 and OBD2

The history of On-board Diagnostics goes back to the 1960s when several organizations started discussing the necessity of having the OBD to detect emission failures.

Specifically, the organizations that supported it were the California Air Resources Board (CARB), the International Organization for Standardization (ISO), the Environmental Protection Agency (EPA), and the Society of Automotive Engineers (SAE).

In 1982, CARB began developing regulations requiring all vehicles to have an OBD port.

Up until recently, the UN commissioned the ISO to develop the WWH-OBD standard, however, it is currently being defined. More on this subject will come out soon.

The AutoPi TMU device and OBD2

The AutoPi TMU device can communicate with the ECUs in your car, as well as the internal computer system (CAN bus), and for this to work, it connects through the OBD2 port.

Here you will be able to OBD2 data logging by connecting the OBD2 logger to the OBD2 connector. This allows you to send "request frames" and the relevant control unit sends a "response frame" via CAN.

You can decode raw OBD2 response via e.g., OBD2 DBC. Meaning that you can also use a CAN logger that sendsTelematics custom CAN frames as an OBD2 logger.

Please note that cars will vary depending on the model/year of OBD2 PIDs they support.

Do you have a use case regarding your OBD2? Get in touch with us!