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Ultimate OBD2 Guide: Understanding Vehicle Diagnostics

Updated at 16 Feb, 2023

— From novice to expert, our OBD2 guide dives deep into car diagnostic systems. Empower yourself with the know-how to troubleshoot vehicle issues.

Ultimate OBD2 Guide: Understanding Vehicle Diagnostics
Welcome to our simple guide on the OBD2 system. OBD2 became mandatory in all newer cars from 1996, and in the United States in 2021 - 282 million vehicles were registered. So you can imagine how many of today's vehicles are depending on this system for diagnostics. Dive in with us as we uncover its many attributes.

If you're a developer, whether novice or expert, or manage a fleet of vehicles, you understand the importance of consistent maintenance to ensure smooth operations. But, are you familiar with OBD2 and its functionality?

The OBD2 system tracks your vehicle's health and pinpoints problems that might be the cause.

This guide will walk you through everything you need to know about OBD2, highlighting its main features, information, and its key elements.

What is OBD2?

In short, OBD2, or OBD-II, is a diagnostics system found in today's cars and trucks.

It's like the vehicle's health check mechanism, consistently monitoring different parts and systems. When it system detects a potential problem, a light will pop up on your dashboard as an alert.

The OBD2 system gathers crucial information from various sensors throughout the vehicle. The car's engine control unit (ECU), acting as the vehicle's brain, processes this information to pinpoint issues. This could range from problems with the engine, exhaust emisisons, or even fuel efficiency.

For example, if you've ever noticed your fuel consumption becoming less efficient, the OBD2 might identify a faulty oxygen sensor as the culprit, signaling you to address the issue before it worsens.

This is the car's way of telling you, that there is a problem within its system, by showing you the malfunction indicator light on your dashboard.

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How Does OBD2 Work?

OBD2 gathers information from sensors located in your car's engine and other systems.

When it detects an issue, it produces diagnostics trouble codes (DTC). These codes can be read using a OBD2 scanner or vehicle telematics device, helping you understand and fix any vehicle performance hitches.

You connect the telematics device to the OBD2 port, typically found under the car's dashboard, but can be found in other areas as well (seen in the image below).

This port has a standard design that lets the diagnostics device communicate with the car's main computer (CAN bus) and fetch the DTCs.

How Does OBD2 logs data?

The OBD2 system continuously monitors various parameters within the vehicle. As it collects data, it compares this information to pre-set standards.

If any discrepancies or anomalies are detected, the system flags these as potential issues, translating them into DTCs. These codes are then stored within the onboard computer, ready to be accessed by diagnostic tools.

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.

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. This is how you reset DTC codes.

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

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OBD2 and CAN bus Connection

The OBD2 diagnostics act as a higher layer protocol, while the CAN serves as its communication method. The OBD2 standard defines a distint connector, encompassing five main protocols.

Notably, since 1996, the CAN bus has been an essential OBD2 protocol for all vehicles in the U.S. By 2001, Europe mandated all cars to be OBD2 compliant, and this became a requirement in Australia and New Zealand starting 2006.

Is My Car OBD2 Compatible?

If your car is newer than 1996 in the US, or 2001 in the EU, then your car is most likely OBD2 compatible.

The five OBD2 signal protocols

As highlighted earlier, the CAN bus forms the foundation for OBD2 communication in a majority of today's vehicles. Within the OBD2 framework, there are five distinct signaling protocols, with vehicles typically adopting just one of them.

  • 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.

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The OBD2 Connector and Pinout

The OBD2 connector allows for easy data retrieval from your vehicle. The AutoPi TMU male connector pinout (here's how it looks like) is designed to interface with the female OBD2 16-pin (2x8) J1962 connector, which is a universal hardware interface.

Unlike OBD1 connector, often found near the hood, the OBD2 connector is commenly positioned within 2 feet (0.61m) of the steering wheel. Below is a detailed image of the OBD2 female connector pinout.

illustration of the OBD pinouts

Quick overview of the OBD2 Port pinouts

The OBD2 port features a configuration of 16 pins, each tailored for a unique role within the system:

  • Pins 4 and 5 serve a fundamental purpose: they provide grounding to ensure safe and accurate data transmission.

  • For direct communication with the vehicle's main computer system, pins 2 and 10 come into play, specifically communicating with the SAE J1850 BUS+.

  • Central to many diagnostics processes, pins 6 and 14 are essential. They establish a connection to the CAN bus, a crucial communication channel outlined by the ISO 15765-4 standard.

Where Can I Find the OBD2 Port?

Generally, you will find the OBD2 port under the dashboard panel and near the steering wheel.

If you're wondering, "Where exactly is my OBD2 port?", then we have made an image below that gives a clear representation.

Most often, it's located beneath the dashboard and the steering wheel, as indicated by numbers 1-3 in the illustration. However, certain car models might have the port in alternative locations, as highlighted by numbers 4-9 in the depiction.

Illustration of the places where the OBD2 port is located in the car

In this Youtube video, we have showcased how to find the OBD2 port and how to connect your AutoPi TMU device to the OBD2 port.

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.


1968: VW introduced the first OBD computer system with scanning capability.

1975: Datsun began using onboard computers in consumer vehicles.

1980: GM implemented an interface and protocol to test the Engine Control Module (ECM).

1988: CARB required all vehicles sold in California from 1988 and newer, to have a simple OBD capability as a minimum.

1994: CARB pushed the requirement further and issued the OBD2 specification in all vehicles sold in California from 1996.

1996: All cars sold in the US needed to be OBD2 compatible.

2001: EU made it mandatory for manufacturers to include OBD2 in all gasoline vehicles sold in the EU.

2004: EU made it mandatory for manufacturers to include OBD2 in all diesel vehicles sold in the EU.

2006: All vehicles manufactured in Australia and New Zealand were required to be OBD2 compatible.

2008: All vehicles sold in the US were required to use the signaling standard ISO 15765-4 (CAN).

Infographic about the history of On-Board-Diagnostics

OBD1 vs. OBD2

OBD, or OBD1, was used during the earlier years of the car manufacturing industry and was used to connect to the console of a car, while OBD2 (OBD-II) was introduced in car models produced in the early 1990s, and is remotely connected to the vehicle.

OBD2 is an advanced version of OBD1 and offers better signaling protocols and messaging formats. Furthermore, it provides better results for vehicle parameters when used in the emission control system.

Infographic explaning the differences between OBD1 and OBD2

The AutoPi IoT telematics 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 sends custom CAN frames as an OBD2 logger.

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

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